what cp is good to start evolving monsters? or is it different for each one?

only level 12 atm highest cp is my snorlax I got at level 9 (first 10k egg) lol =P

also is it better to power up the cp then evolve or wait for the evolves then power up cp?

You'll start finding higher cp pokemon as you level up. If you plan to fight for gyms, it's probably better to wait. But if you're just wanting more for your pokedex, or you just like evolved pokemon have at it.

As far as power up first or evolve...if you can't tell what the level is for IV you can power up twice to make sure you have proper level for IV rater.

If you are wanting good pokemon only evolve those with high IV and then only power up those that have the proper moves.

Steps:

Find nice IV -> evolve -> if proper moves -> power up.

Always check proper moves when powering up your Pokémon!

stuff is important in this order;

IVS->moveset->CP

most people don't care about IVS so the next most important thing is to see what the moveset will be using the smallest amount of candies

(in other words evolve your pokemon first, that way if their moves are shit [like a nidoking with fury cutter] you don't waste a bunch of stardust and candies powering him up first)

Always evolve, as to level up your player, so you can find better pokemon. Never power up until like 1k++ cp and good moveset/iv