mouse: I'm using Logitech G9x myself, but it's (I mean its) price is pretty high now. Roccat Kova+ seems pretty good too.
tablet: I have a wacom ctl-480 myself, and I definitely recommend this. In fact, wacom is the brand you're looking for.
The other Chinese tablets need to either charge the pen or put a battery into it, that's a bit troublesome, let alone the pen would be too heavy for rapid response.
Wacom tablets don't have such problem, their pen requires no power at all. Whenever you wanna use the tablet just grab the pen and you're good to go.
As for the models, don't buy the ones with touch support if you don't need it elsewhere. It's useless for osu.
If you wanna do some drawing, then you may look for some mid-sized tablets, otherwise the small-sized models are big enough for this game.
Edit: spelling correction... I'm a bit obsessed with this orz