I'm by no means an expert in this stuff, and while I don't do much PvP in SWTOR, do I have a MMO gaming background so I'll try to answer your questions to the best of my ability and personal experience.
Also, this doesn't particularly apply to tanks (or PvE for that matter, you can do fine in those with clicking, imo), since I've never played one. It's more of a list of general concepts.
1: Will this impair my moving around? I use WASD to move, which is slower to turn and such, but also means I can back peddle and use abilities etc. which I can't do with a mouse, as I'd have to turn around and run
First things first, I'd advise you to bind A and D to strafing
instead of turning
. You'll be using your right mouse button to turn, W to run and S to back peddle (some PvP-people even unbound S, since back peddling is slower than turning around and running, but I never did this and I performed allright, so don't worry about it).
So the main way to move around is M2 + WASD. Just think of your mouse as a tool to purely manipulate the camera. Imagine you don't even have
2: What are the best keys to use to bind abilities? And how will this affect playing different classes?
I usually have the following keys bound in MMOs across all of my characters;
Shift + 1-6
Shift + Q,E,R,T,F,G,X,C,V
There's some other things you could bind to, too, along with ctrl and alt modifiers, but I find the above are more than enough in SWTOR. Also, while it might seem intimidating at first, I suggest to bind every single ability
to a hotkey. This way, you'll maximize the time your mouse is acting as a "camera" instead of a "cursor", making learning faster and improving your game rapidly.
3: Will I have to buy a better keyboard and mouse? I don't want to have to spend £200+ for amazing keyboard and mouse, just for them to not help at all.
As long as you're comfortable using what you've got, you're golden. Buying overpriced "gaming" keyboards and mice won't magically make you any better at the game.
That is how I always play and move around, be it PvE, PvP or solo. Hope I helped, at least a little bit.