This is my first guide here. Currently pulling in ~50k sins per Amnesia.
I didn't make any guides for my early progress. Sorry about that. But this is what I can tell you about the Spider >> Aztec levels. (and now from Aztec to end game...)

If you haven't reached Spider yet... follow this short guide

• [1] Reset.
  Hourly. Daily. Once at every meal time... I don't care what routine you get into. Just RESET.
  Again, and Again, and Again.
  
  
• [2] Don't grind.
  You used all of your skills and they are on a 15 minute cool down? and everything slowed to a crawl while you wait for the skills to be up again?? Sounds like it is time to reset.
  Seriously, resetting often is better than the grind. Just keep resetting.
  
  
• [3] Save your Sins
  Every Sin in the bank is bonus damage.
  There is a fine balance between the benefit from buying illnesses and the benefit from just banking everything. But trust me that 99% of the time, that balance is in favour of just banking your Sins.
  
  
• [4] Set a target.
  100,000 Sins? Get to that before buying anything.
  Get to 100,000 and then spend the next few resets shopping.
  But Never Go Under The Target Amount !!!
  Then set a higher target. 500k? 1 million? 1.5 million?
  
  
• [5] Reset some more.
  More resets = more Sins.
  More sins = more damage.
  More damage = better run on next reset.
  = more sins.....

The "Spider wall" is the biggest wall up to this point. It takes A LOT of effort to be able to get to the spider, but it is worth it. There are plenty of other guides instructing you how to get to the spider, so my guide if focused for players who can comfortably get to the Spider on a regular basis.
Once you get the Spider, put EVERY enhancement on the spider (minus any that you need to reach the Spider). The spider will carry you.

If you shuffle around your minion enhancements so that 50% are on Spider and 50% are on Troglodyte then you will see the damage between these two go back and forth for which is giving more DPS. (if memory serves me correctly)
Troglodyte LVL 1-100 will see the Troglodyte dish out more damage.
Troglodyte LVL 100-200 will see the Spider dish out more damage.
Troglodyte LVL 200-300 will see a lot of back and forth. Lvl up one and it has the higher DPS, level up the other and it will take the lead.
Troglodyte LVL300+ will see the Spider take the lead and stay there.

I actually just recomend putting ALL enhancements on the spider and leaving them there. Why pay for 2 minions at 50% power each when you can pay for 1 minion at 100% power.
By this stage you should be getting around 10k sins

Kain is useless. Just focus on farming the Spider and Troglodyte.
By the time you would have got lvl400 Kain, you should be able to afford lvl 1000 Troglodyte. That will give Troglodyte another boost (x10) that makes it close to Spider standards again... but only for a short while.

Orezan is like Kain, useless.
By this stage you will be forgetting what progress feels like.
Just farm, upgrade, farm, upgrade, reset, start again.

But don't give up. You will begin to notice your Sins after each reset slowly increase. From 10k to 11k, to 12k... 13k... 15k.
In addition to this, you might go up high enough levels (every 200 chambers) to get a permanent 5% boost to damage.

5.0e107 seems like a lot... until you get there.
You should be able to buy your first Aztec shortly after reaching lvl 2075 on the Spider.

The Aztec is the first real progress you have made in a while. The first minion that stands any hope of dethroneing the Spider as the main DPS unit.
Lvl 1-100 on Aztec, you should upgrade the Aztec.
Lvl 100-200 on Aztec, you should upgrade the Aztec unless you can get a full 25 levels on the Spider.
Lvl 200+ on Aztec, the Aztec is the better investment.

Getting to Aztec after a grind in order to get 5% boost from achievements is easy.
Getting to Aztec after every reset is difficult.

The first time you reach the Aztec, ALL of your enchantments should be on the Spider.
As time goes on you will get stronger (thank to Sins and illnesses), and as this happens you may slowly transition all of your enchantments from the Spider to the Aztec.

Aztec is the new Spider.

Nancy, and Marionette. They all follow the same trend.

All of your enchantments will be on the Aztec, around Aztec level 450 you will buy your first Nancy.
Nancy will give you 0.1%-2% of your overall power. You will think it is the next step... but it isn't.
Every 25 levels of Aztec raises it's damage output by 400%. This easily outpaces the first 200 levels of Nancy. And in doing so, cements Aztec as the preferred choice.

Rinse and repeat for Marionette.

This information can be put to good use. If you're about to go away from the computer for a while (sleep?) and can't afford the next 25 levels on Aztec, then buying a few levels of Marionette is worth the ~2% boost for the short run.

The Xonoid is the same as Troglodyte.
From Xonoid level 0 to 100 it is better to favor Xonoid.
From Xonoid level 100 to 200 it is better to favor Aztec.
I'm not quite up to Xonoid level 200 to 300, but we can assume it will swing back and forth for a while before ending with Aztec as the better choice.

Currently resetting at floor 2000 @ 42k sins on my fast runs, and pushing 2200 @ 50k sins on my long runs. As it stands, Spider is the biggest step, Aztec is the next step until the end game: Azathot.

1- Upgrading damage illnesses is not worth it.
You literally get more damage from keeping the teeth (just be sure to keep the teeth and not spend it on other things.)

2- Time left to kill the boss is either really good, or really bad.
Good if you want to grind up higher levels
Bad if you want to grind by idleing. Because killing a boss really slowly also means killing other monsters really slowly. And idling works better if you kill the monsters really quickly (so as to get more chests)

3- Teeth from broken jaw is good
4- Teeth grown while idle is better.
5- Teeth from Chests is best.

6- whenever you want to make the transition from 1 DPS unit to another, or if are grinding into deep chambers to unlock achievements, or to just kill that last boss before resetting... Crit is your friend.

7- The upgrades with a limit on how many you can purchase are a MUST HAVE.
But this guide is from Spider to Aztec. You should be well and truly past that.