Warm welcome to FT. Thanks for joining us and I'm sure one of our ambassadors will be along in a moment to give you a full welcome
From what you've said above, assuming I've understood correctly:
* You won't be able to upgrade with miles.
* At check in, you can ask if there are any promotional upgrades (with money) available to World Traveller Plus.
* BA doesn't do gate upgrades, for miles or for money.