Sha,

with UK passport : you fly, you land, you score - simple.

Fly with anyone you choose, be sure to have credit card to pay QR 100 for your tourist visa at Immigration after you land, once in Qatar your employer (a school / college, it would seem)will do the needful to change your TV to RP.

Your employer should really be advising you on all of this. Who will you be working for?

Good luck.