Strategy help?(Ren. Start)

A friend and I have considered an MP game, with me as Germany and him as England. His strategy is to invade CS's to gain exotic footholds, whilst I have no idea as to how i can counter this. Can anyone give me a hand? (Renaissance Start, Prince/King)
Also, is it a good idea to invade large numbers of city-states? I've recently read a thread where someone stated that everyone turned against him for attacking a CS.

Each DoW and taking out any state (major or city state) gives you diplomatic hit.
And attacking two (? I'm not sure) city states makes the rest hate you.

So It's either 0-1 or all.

Countermoves that comes into mind: give CS units (so these units fight against your enemy without you paying upkeep), attack his cities when he attack CS. If it's overseas, harras his units when he is crossing. Send raiding parties to plunder his improvements when he is attacking someone.