The available followers can be a mixed bag, and a lot of their usefulness depends on how well they mesh with your character's own style of combat.
Do you want someone who will charge into a fight while you hang back and do your own stuff? Hire someone like Erik the Slayer or Stenvar - a warrior type. Do you want someone who will also hang back and use ranged attacks? Hire a destruction mage like Marcurio, or someone who will use a bow if you give them one. Jenassa is a good archer type altho in my experience any "warrior" type hireling will use a bow if he/she has one. Belrand is a spellsword who will use both magic and melee weapons if you want someone who can vary it up a little.
Do you prefer sneaking around? Marcurio has decent sneak skills, IIRC Jenassa does as well.
If you give them the standard Restore Health potions found in loot or that you purchase from merchants, they will use them when they need to. Not so sure about the homemade stuff; I've never tried it and the pre-made ones are so easy to come by that I just give those to my followers and keep my homemade brews for myself.
As to number, unless you're on PC and use mods to alter the vanilla game, you can only have one (non-animal) follower at a time.
Given your character's skillset you might want to find a follower who will be quick about taking out your enemies, in order to provide you with a corpse to reanimate for extra assistance against multiple attackers.