Depending on which model year you end up with will effect the spec as BMW make some stuff standard after a while when previously it was an option. The biggest difference to be aware of is the 'sport' and 'non-sport' versions. The latter have no abs or TC and should be significantly cheaper than the sport version. QS I think was always standard but it's easily identifiable by looking at the gear selector for the module. Modes wise, it's rain, sport, race and slick. They all come with all of them (the MY15/16/17 has an option which would lose the slick mode but that's not in your budget, just sayin). Slick is available with the red slick plug installed under the rider seat (have a look at an online s1000rr manual for the details). If the bike you look at hasn't got slick available then a plug is a few quid, some owners never installed the plug to enable slick for fear of death or something like that but the rest of us have survived with it plugged in lol. Heated grips have always been an option, as have been pillion seat and pegs, I can't think of much else to worry about on them.
My advice would be to buy one with full BMW service history if possible, and if it's from a BMW dealer you get a comprehensive warranty for piece of mind. If you feel inclined to, Simon at Alan Jeffries in Shipley should be able to point you in the right direction and should do you a good deal if you mention the forum (they're honour bound to look after us).
If you are looking at a bike and want to know the spec, Tim at Lind has offered to check details against registration plates, he's a vendor on here.
Also Stephen in Bradford is a good independent BMW workshop if you choose to avoid the stealers.
So hopefully that lot should be of some help?