1. from what I've seen, most plugins are compatible with tekkit
2. IC2 seems to be the only mod with a config file of any use, it gives you options to disable the crafting of some IC2 items and afew other cool things
1. refer to next point
2. you need a tekkit client to play on a tekkit server yes, as long as the server and the client are running the same build they will be able to connect
1. simple, just don't have more than one world
2. permissions is a plugin, plugins work with tekkit
P.S. don't sign your posts, they don't like it