Building bookshelf speakers

[martix_agent]

this is my first post ever here and i think it's going to be a doosie! I chose this site because it's smaller yet seems to have some solid members. Please bear with me as I attempt to explain what I'm trying to accomplish.

Over the winter I built a sub box for the heck of it and was surprised how much fun it was. It's a 12 inch driver powered by a 200w amplifier with high pass filters for the speakers and a variable range from..well i'm not sure, I'm not feeling up to pulling it away from the wall. Finally, it's tuned somewhere around 27 hertz. I had to fudge a few things when i got it all cut out because my port would have run into the driver if I had used the orgional plans...which is weird because I though I had it all calculated correctly.

There's my background, now onto the juicy stuff.

I still have half of the MFD board that I bought to build that speaker and now I'm hunting for good bookshelf speakers. Since I've got some extra left over I figured why not build my own bookshelf speakers? I have about a zillion questions before i even start believing I can possibly do it though.

I'm looking for these to be my main speakers, currently all i have is the sub i built that i've been using on my computer. my computer speakers died and I pick up a reciever/amplifier with full surround features so I figured it's a good time to start working on getting a surround system running. it's a 240W pioneer for I'd say 5ish years ago maybe. My parents got a new reciever with better things and gave me this one.

Since I have a sub already, What do I need in these speakers?
I'm also wondering if there's a noticeable difference between 3-way and 2-way?
I understand what crossovers do and why they are needed, but how do i know what I need in a crossover?
Do you know of any places where I can get some basic box dimensions? that was the hardest for me when i built my sub box, finding information that was reliable. seems every place says something different.
Do i need to use the same speakers for both main speakers and the center speaker?(whihc i'm also considering building, if what i get is cheap enough and i have enough MFD leftover.) What about the rear speakers? I'm unsure what this will be used for more, movies or music. I'm not sure if that makes a difference or not.

Lastly my budget is around $120ish, i may be able to go a bit higher though, if I feel it's worth it.

I really like buying from parts express, as they have an incredible selection and ship to me very quickly as they're only a few hours away. I believe that's the sit I'll be using to get my things unless I can be convinced otherwise.