Several Questions

I will try...
1) That depends on how much time you're willing to devote to an abandoned engine falling behind the times for lack of development. It also depends on what any of it is worth to you, personally (or sentimentally.) Others can play it if you build it, though there are still many unforgivable bugs. I, myself, still enjoy playing with it from time to time.
2) There are two separate GUI executables in RCCE 2.0 because of issues with that. For the client, try changing the settings, exiting, and then restarting. I'm not really sure, though, it's been about four years for me.
3) These are still around, if you ask the right people. I, personally, refuse to redistribute the intellectual property of others, though, even abandonware, and most others in this community feel the same. It's just not worth it.
4) Search Google for "free 3d models," "free .b3d models," (or .x.) There are several sites out there, though some models may have to be converted in either Blender or Fragmotion to be used in Realm Crafter if they're not .b3d, .x, or .3ds. Turbosquid has lots of free and paid models. Arteria 3D and 3Dfoin also have fairly affordable models that look rather pretty.
5) Blitz.