Colony Survival versions before 0.9

SPOILER ALERT:
Just in case some of the information are something you want to discover yourself.

First some game mechanics facts to be aware of and what calculations are based on, to find an optimal ratio guards vs colonists.
Any mods (modification modules) can change the behavior described below.
Game time is 120 times faster than “real time”. So 24 hours in game time is 12 minutes (720 seconds) real time.
A night lasts for 270 seconds real time.
Zeds and Colonists do not jump or move diagonally. Move only 1 block up or down or flat.

On normal difficulty each colonist spawns 2 monsters/zombies (Zeds) during a night, ratio 2:1.
Uncertain if the total spawn count subtracts any existing ones, but it seems like it.
Spawn spots are relative to your characters position and amount of Zeds.
Spawns with roughly 1 seconds apart from each spot at the same time, random health and speed.
Spawn spots are within 75-200 blocks from the Banner, Banner research expands safe zone, so can change up to 101 (from 75).
Max path is 2000 blocks to banner, siege mode if longer distance.
Zeds can have one of 3 health points (HP); 100, 300, 500.
Zeds can have one of 3 speeds; Walk, Fast, and Run. Walk is roughly 1.5 blocks per second, Fast 2, Run 2.5.
Zeds do not die to sun or age, only from guards and players.
Zeds are not “solid”, they can walk through each other.
Zeds targets the Banner, unless the player or colonists is closer.
Zeds can only attack if can move to the block the player or colonist (or banner) stands on in one step, adjacent.

A guard’s watch, night or day, lasts for 450 seconds. Sleeps for 270 seconds. Depends on that there are still Zeds around.
Current weapons info; Name, damage, reload, range:
Slinger 50 3 12
Bow 100 5 20
Crossbow 300 8 25
Matchlock 500 12 30
Target logic are that they take down 1 shot zeds first. Crossbow will have the priority 300 100 500, Matchlock 500 300 100, Bow and Slinger 100 300 500. The targeting happens when a guard is ready to fire, selects a Zed is in range regardless of what comes next, since they do not “see” past the range and unable to plan or cooperate. That way “waste” of abilities of take downs will happen.
Guards seems to be able to shoot and have line-of-sight through other guards, since not solid (your character can walk through them).

To figure out roughly how many guards are needed for a certain amount of colonists, some key information of game mechanics ought to be understood. That are how many monsters can a guard with a certain weapon take out during a watch. So the 2 most important factors are HP of Zeds and a weapons Damage per Reload (in seconds).
Reload time give how many times a guard can fire during a watch.
Damage gives how many shots are needed to take down a Zed.
Range is secondary.
Ammo production to keep up should be obvious. The amount of Zeds give the stockpile needed, not the amount of Guards.
Weapon types can give the needed length of the defense structure (maze) too.
Speed of zeds have little effect, just adds some more blocks to a maze to be “safe”.
Mixing night and day guards just give that a maze can be shortened.
It could take some time before the first Zed arrives within a guards range, reducing the amount of Zeds that is possible to take out.
But if the maze is long enough so the guards can start shooting straight away, then almost no waste of time (if line-of-sight all the time).
Guards need no crates to get ammo or weapons.
It seems that sometimes Guards waste ammo (and time) by taking out a Zed that already have gotten shot by another Guard.

Now you have the main info to calculate the ratio guards vs colonists. But since the health of the zeds are random, the answer will be an average one for an optimized defense, where to assume an even mix of each health. If to be extra sure, then assume most/all zeds have max health.
Bear in mind that even if Matchlock seems the best, it will require more guards due to slow reload time, wasting damage output on zeds with lower health.

Each weapon requires certain time to take out each of the health types of zeds after just finished another.
Weapon, time in seconds (100, 300, 500) = total seconds needed to take out one of each (3 zeds).
Slinger 6 18 30 = 54
Bow 5 15 25 = 45
Crossbow 8 8 16 = 32
Matchlock 12 12 12 = 36

So during a watch with 3 mixed guards, no Slingshot 24, 30 42 36 = 109, divided by zed : colonist ratio and 3 = 18 (rounded down), giving the ratio 1:18. 1 guard and 18 colonists including the guard, if to be pretty safe with a short maze, where all zeds are removed. Could be rounded up due to first shot does not need reload. BUT, this is average simplified math.

More correct is to use the amount of zeds, 1/3 of each of the total. Say 36 * 3 = 108.
If assume the zeds are taken out the most efficient way, the time is calculated different.
Bow 5 * 36 = 180 seconds
Crossbow 8 * 36 = 288
Matchlock 12 * 36 = 432
Since a watch can go on for 450 seconds, the guards will have nothing to do rest of the time, meaning the guards can handle more zeds than the average 1:18 ratio. Now you can start adding sets of zeds of each health, where they still take out the zeds in the most efficient way (the equation for this we skip, more difficult math). Assume Crossbow targets 500 before Bow are able to, using 16 seconds. Bow uses 20 seconds to take out 100 and 300, until Bow guard goes to bed.
111 114 117 120 123 126 129 132 135 138 141 144 147 150 153 156
185 190 210 230 250 270 290 310 330 350 370 390 410 430 450 Bed
294 304 320 336 352 268 284 300 316 332 348 364 380 396 412 444 Bed
444 456 Bed
So the adjusted ratio improves to 1:26 (156/6)

Can use an easy way by average calculations:
Using Damage per Reload (DPR) seconds (damage divided by reload time)
Bow 20
Crossbow 37.5
Matchlock 41.66
Average is 33 (If have an even mix of those 3 weapon types, else have to a more thorough calculation)
Average HP of 1 Zed within an even mix of Zeds is 300 (500+300+100 / 3)
Giving average 9 seconds to take out a Zed. So 1 of the mixed guards can take out 50 Zeds during a watch, giving a guards vs colonist ratio of 1:25.

Crossbow becomes the average best, if to have most of one type of weapon. Since as the mixed average DPR (32 vs 33).
Matchlock wastes a lot of time on low HP Zeds, but the range can compensate. Ammo is more expensive too, needs most work and resources.
Slinger is just a cheap starter weapon, avoid it as soon as possible.
Bow is OK if in a mix, or until have Crossbow ammo surplus.


Some details helping in how to set up a defense structure, normally a maze system or several.

A bed can have a solid block above the foot end. Also no need for a solid block below the foot end.
A guard need 5-8 blocks space (3D), where they stand (3 blocks) and a bed (2-5b). Can make it so most beds need 1 "solid" block, by using stairs, where the foot end have part of a bed underneath (and above).
Assume a Zed attacks the head end, so could let a foot end be in the path of Zeds at high of their head.
Or the foot end could occupy the same space as a guards head.
Beds and other guards should not block line-of-sight for guards, since not solid.
Guards can shoot in any direction as long as line-of-sight and within range. Good aim, so Zed speed should not be an issue.
The speed of a running Zed give a minimum distance of blocks to be very safe: 450 * 2.5 = 1125. Since only a few runs and assume follow a 1:25 ratio, the sleep period gives 675 blocks. Average becomes 900 blocks.

After my ratio 1:25, 800 mixed guards should be able to take out 20000 Zeds, protecting 10000 colonists on normal difficulty.

Minimum space required are 4000 blocks. Maze still the same 900 (roughly) moving distance, where space needed is 2700 blocks (zeds 2 blocks height). So roughly 6700 blocks would be needed for the defense structure.

The smallest banner safe zone is a cube of 30x30x30, giving 27000 blocks to create a design. If have the outer part of the maze just outside the safe zone (no safe zone research), additional 3600 (roughly) more block space can be used, and OK for zed to spawn on.
The “empty” space for the needed line-of-sight should be pretty easy to fit in.