My two penneth worth...
- check in desk as [B]hotwingz[B] says it would be open from 0500! so yes.
- Bag drop before you board you BRU flight - i'd say almost certainly no. I know OWE helps but in my experience unless you're J/F or even a QR Plat (i know OWE is equivalent!) they are much much less likely to help.
-Baggage allowance as remdk has said it actually would vary if you check them in LHR onwards or from BRU ... i think! But my opinion is that honestly unless you're really trying to push the boundaries piece or weight wise you'll be fine with 2 good size and weight bags!
- I would also say that you MAY be able to (I would certainly try!) to interline from BRU or LHR all the way through to HKG (unless you're hoping to stop off for a few days at any time) as they're all OW airlines.