If you want to race, and are starting from scratch why not start with 29er wheels? Hope Hoops with Crest rims are popular and about £300!
Drivetrain – XT is logical and can be had from Germany for around £500 inc brakes
Frame – on one Have a number of good options but the Inbred is a bit heavy. If you have more cash spend it on something sexy. To and Carbon are popular.
Forks – Fox, Rockshox and Magira are all good. If you go with Fox get the Kashima coated ones.
Components – Easton and Thomson are nice but there are plenty of others out there across a range of prices.
You don’t need a dropper post. And don’t forget a nice light saddle.
Lock on grips are worth the effort and for tyres either some Schwalbe Rocket
Ron or Maybe Kenda Slant 6. Running tubeless of course.
Headset – Chris King is nice.
That’s what I would do. Or just go and buy a Scott Scale, Cube Reaction or Specialized Stumpjumper off the shelf.