If you are wondering how CPs affect your stat pools, each point you put in to the red tree will increase your health, green tree increases stam and blue tree increases mag.
First, you want to use food. Probably a blue max health+stamina one or the purple max health+max stamina+stam regeneration one. Basically you always want to have food buff active, blue food is super cheap anyway. 13k unbuffered sounds fine(assuming that's without food). If you still feel it's too low even with food, use some health enchants on your gear, get healthy jewelry or redistribute some attribute points into health. Basically you want something like 17-20k health for PvE(buffed with food), higher than that is really overkill unless you're tanking(in which case you'll want 25k+).
Second, Cyrodiil buffs your health automatically just for being there so you don't due quite so fast(listed under Battle Spirit buff I believe), and buffs it even more if your alliance gets Emperor. CP have no bearing on that, would have same effect for Cyrodiil as they would out of it(aside from no cp campaigns where they'd obviously be disabled so you'd have less stats overall, but probably still bit more health than in PvE due to the Battle Spirit buff).
Third, as been said above, every cp in corresponding tree will increase your max stat ever so slightly(green increases stamina, blue magicka, red health). Aside from that they do not increase your max stats(but they do give you other nice things). But you can't control which type of constellations you want points into, you always get 1 for blue, 1 for red, 1 for green, rinse and repeat(might be different order but the idea is the same). You should obviously spend all of your champion points, no reason not to, for specific perks most useful for your build is suggest looking it up, most builds these days including cp distribution.