Sleem Satiety?
 

How are you suppose to activate Sleem to serve you, do you have to just have snakes in your army and wait or what?

Get royal snakes or poisonous spiders in your army and talk to him.

Run to the Marsh, buy 17 royal snakes there and feed 'em to Sleem.

Do rage spirits gain experience only if you use them in combat or is it automatically if they are activated to serve you?

only by using their abilities :)

btw. don't give him royalsnakes
they're just too good
buy him something weaker

Sorry, I probably did not understand you fully - by "if they are activated to serve you" do you mean in speak dialougue?

If so - than the speak dialogue is only for activating them (only the first 2 ones - sword guy, sleem) and for fun from knowing their history/ or have a nice talk.

Also good to now is that you gain full XP only in first 10 round, 50% in next 10 round, after round 20 you get nothing, nada, nist

Also know that if enemy is rated too low in comparissino difficulty (weak for instance) you get nearly zero or even zero EXP for your spirits - so fighting very weak enemies and using your evil shoal, or underground spikes will not have any other effect than harming you enemy - but don't expend to make new level for your spirit :)

With mage rounds never last more than 4.

Do you get Lina and Reaper after level 10 of your character?

Also I was wondering do you ever get resurrection spell?

Ressurection spell : It is random as long I know - but I heard a trick for this - visit the Marchan Swamps priest - if you talk to him in the "right" way you should get ressurection (but this probably works only for paladin)
Otherwise - you just need to count on your luck (and the "start-game-lucky-randomize-roll" )

Lina - you get her as third in the row - you get her when following the main quest - it is not based on your level, but on you main quest progression - as there is and some specific device somewhere in some specific land, where you can get ... later...

Reaper - the same as Lina - just this bony-one fellow is even little bit further in da game - again only by following the main quest (the usual stuff - talking to right people, and progressing in the CROWN quest)

but to get reaper u have to fight and free the bogacho castle in teron mines
that's not rly easy if u have shitty troops :)

Why does everyone keep mentioning Royal snakes for Sleem? Can't you just feed him some of the garden variety snakes? IIRC, one of the level 2 snakes is also poisonous.