"Such insolence... such arrogance... must be PUNISHED!"
You could make a new character and leveling when forcing you to use keybindings, I think it's easier to get used to it that way, you don't have to go all the way to 90 but maybe 50-60.
Keybinds > clicking. There's just no reason you'd take a "good" clicker over a keybinded player. Yes, you will "do fine" clicking. If you're aiming for doing fine, click away. If you're aiming for awesome, keybinds are the way to go.
I'm not going to argue with anyone about that, so don't reply to this post in that regard.
Set up keybinds with your most frequently used abilities close to WASD,
Personally, I have:
Starfire on E
Starsurge on Shift-E
Wrath on Q
Starfall on 3
Dots on 1 & 2
Figure out what works best for you! But don't judge the bindings after 10 minutes of play - You're not gonna get into it after one bossfight.
You want your utility cooldowns fairly far away from wasd, but not too awkward to press - for example, I have rebirth on F2, Stampeding Roar on Shift-4 and so on.
Keep your big cds where you're not gonna accidentaly press them.
The only way to get used to it is to force yourself into it.
What better way to practice keybinds than lfr?
Get in there and use a lot of stuff - if you see Some mobs tank didn't bother to pick up chasing the healer, throw out a Ursol's. If you see some guys getting low, help out with a tranq etc. Remember you're not there to top meters or save the day with a perfect timed tranq, you're there to practice keybinds.
Whatever you do - do NOT click stuff!
I think it took me an hour or so to get the basics into my head when I switched back in the day. You can do it, it's all about muscle memory!
I hope I helped you! Good luck OP