Hi there G4merSylver, let me see if I can make this easy:
1.) Yes, player cap is completely dependent on your game’s setup and the hardware it runs on. This is true for most questions of scale (max players, max world size, polycount per object, etc)
2.) Sure can: Link
2.1) Another Link and an entire Playlist of Videos
3.) Yes, you have even more options to work with in code
3.1.) The next link should have some code snippets to copy/paste
3.2.) Code Tutorial: LINK
4.) Not really, MMO games are not very simple and can be tackled in so many different ways. Check out this thread with a response from our CEO Tim Sweeney about it.
4.1.) I don’t really have anything for this, you may want to search the wiki and forums for more info. Making something as big and complex as an MMO involves a lot of trial and error.