1) London Drugs likely no longer even has any stock of the 330. 7150s have faster processors in them, and thus, it's likely you'd have a better experience with them. If you can get the 330s, they do still work, but the UI can be a bit sluggish with them at times. You may also have trouble getting them to give you 5 HD with them.
2) This is kind of a crapshoot, because as far as I know, there is no official word on this either way (thus the variance of answers you've gotten). From what I've been able to gather, it requires a model newer than the 330/430 series (like the 7150s) and a very good quality line all the way to your residence. As far as Internet plan, from what I can tell, 25 may work but your Internet speeds may be impacted if you're running a lot of concurrent HD feeds as it's an actual limitation to the technology. 50/10 uses two lines bonded together in most residences, which provides for more bandwidth. As a result, they may be hesitant to let you do it on 25. I think it comes down to a call from their network team.
3) I'm not aware of any way to do this short of it being on a separate account, but I don't know for sure.