I'd answer the second part on a case by case basis.
In answer to the first part, I'd be tempted to say that active would be better since the system will be designed to work together but OTOH you can use what you have now and get a better amp later, which will allow you to get better monitors now.
I got a pair of Tannoy PBM 6.5's for $100 and they're great.
I'm not saying that these are the exact monitors you want, but for example: http://search.ebay.com/search/search...6.5&category0=
The HF drivers are Vifa's which I get replacements from Speaker City on Lankershim in North Hollywood, Ca. I think they're $35 a pair or something. Best to have spares for whatever you use.