I am interest move my server to RackShack, they give Raq4 with cheap cost (US$99/month) and high traffics, I hear RS give 8 ip address only for free...is this enough for 200 domains? If using 1 ip for several domains, how many ideal domains on there?

It's more than enough.
You can basicly host hundreds on one IP.
You only need an IP based site if you want to have SSL access or an anonymous FTP.

Good luck :)