answers as asked:
1) be sure that the Cosmos you want to buy qualifies for warranty support if that is important to you.
2) what specific problems are you referring to?
3) You need to remain connected to the PC, either tethered or wirelessly. The room-space-limits only refer to moving around in that area to play a game that involves action by player, such as the Lab. To watch a movie on the Cosmos (I do not know why you'd want to do so), you only need to stay in connection range.