At level 50 you have 683 points to spend on the 8 skills. You will NOT be able to max them all, but you can respec with an item dropped randomly (so far I got it from helltyr clubbers).
Anything you have built with a skill you no longer have will remain and be useable.

The cost to advance is as follows:


You can max out at most 6 skills, with some leftover.

Of course if you play with a group you can max whatever you want, as long as there's at least one type of skill maxed out across everyone.
Usually level 10 is where you get the really useful stuff.

That said, some skills have really nice perks at specific levels.

Must have

• Lvl 3: Stove - useful when you're out hunting and want to cook some meat. Compared to the campfire you can pick it up after use. Most high level cooking recipes need a stove.
  
• Lvl 4: Forge - needed to make a lot of stuff, including almost all the weapons and tools. Useful to have to put up a farming spot to replenish picks, knives and axes as they break. NB: you cannot pick up forges, only move them.
  
• Lvl 4: Bed - If you put down a bed it will act as a possible respawn point.

Nice to have

• Lvl 8: Garage - To put your vehicles in and protect them.
  
• Lvl 10: Water tower - It will slowly fill up with water, so you can put your base far from a lake
  
• Lvl 10: Silo - The biggest "crate" object.

Must have

• Lvl 3: Elctrode plates, Wires, Batteries - Needed to craft beam weapon ammunition. Given how much you'll use ammo it's better to at least have this much.

Nice to have

• Lvl 5: Refrigerator - It will delay the spoiler time on perishables. It's a static object, so you need a base to put it in. Also gives Industrial station, needed for other advanced recipes in other skill trees, and a static turret for PvP base defence.
  
• Lvl 5: Personal shield - A consumable that will give you some small hp buffer, it stacks but it's costly to make. Once depleted it you will need to make more.
  
• Lvl 7: Crafting Station - Needed to make most advanced armour.
  
• Lvl 10: Off road vehicle - self explanatory
  
• Lvl 10: Genetic engineering station - used to make pets with subsistence skills

It gives a cumulative 3% bonus on melee damage per level, so any amount is nice to have. If you prefer melee max it.
Must have

• Lvl 6: steel knife - best tool for gathering from plants

Nice to have

• Lvl 7: steel axe - best tool for chopping wood, but you can kill lurker chieftains for their axes instead of taking this.
  
• Lvl 10: 30% bonus damage on melee weapons

It gives a cumulative 3% bonus on ranged damage per level, and 1.5% for explosives, so any amount is nice to have.
If you shoot a lot max it, otherwise it does not have any synergy with other trees.

Gives you a cumulative 4% bonus on tool durability each level. Nice to have but not a deal breaker.
Must have

• Lvl 6: - the bare minimum to get a decent pick, and to be able to craft painkilers
  
• Lvl 8: - gives you access to all the important materials and the steel pick, the most powerful tool for mining.

Nice to have

• Lvl 10: farming - at max level you can put down little earth patches to grow seeds in, so you can have e.g. geel in the desert. At the moment the process is somewhat convoluted however. Doubles as nice base onaments.

Gives you a cumulative 5% resistence to hunger and thirst each level, and is used mainly to cook the meat you'll get from monsters. At least some points are good to have, you eat a lot after all.
Must have

• Lvl 2: mortar and pestle - used to make a lot of raw materials
  
• Lvl 4: ngooberry juice - needed to make painkillers

Nice to have

• Lvl 9: Genetically Engineered Setlang - get a dog...cat...spiky thing to follow you around. Requires an item from lvl10 electronics to make.

Gives a cumulative 10 hp and stamina points per level. Max it. Hp restore items are in this tree.

Used to craft armour and bags.
Almost all recipes require a crafting station (lvl7 electronics), it only requires one person in your group to max it. At level 10 you can make the biggest possible backpacks with setlang or lurker hide.