A few points. Just because a lathe will cope with a certain size blank doesn't mean it's ideal or will do it all day long - it's common in advertising to say x" over bed, then lead you to believe it's capable (specially on cheap lathes) of doing it successfully. It's just like the advertising for bandsaws that have a certain depth under the guides - it doesn't necessarily mean you'll cut that thickness of timber.
The power and speed needed is determined by the diameter of the work - low torque, high speed is great for a pen blank, but not for a 30kg bowl blank. As said before, you can turn small stuff on a large lathe but not the converse - if you have the space, go large.
The cost of the lathe is less that the ultimate cost of the ancillaries - I have more than a thousand quid's worth of chucks, jaws and centres, several hundred quid's worth of grinders and jigs and a couple of hundred quid's worth of abrasives and accessories. I haven't even started on tools, and if I actually priced the stuff if would be more than this conservative estimate. Most of this isn't necessary to start with, but don't think you won't end up spending a lot.
If you can find a club, do so - besides gaining knowledge you might pick up a decent lathe a tools for a fair price - people trade up and down. Buy the Rowley book.