Hello. Been in same situation with transferring from full time clicker to full keybinds. You're right, you will see biggest improvement in PVP, especially as melee.
As for getting used to binds, i prefer dummies, absolutely no BG or dungeons. Get someone to party, use party skills while dpsing dummies, move from one to second dummy, use focus cc/interupts on dummy. On BG u will get a lot of downtime with training. OFC its beter when u get some use to binds, but start is best on training dummy.
First of all, i've made all binds in my mind depending how often i use them. U can go a road with few keybindings at start, but for me it was good to bind EVERYTHING like mounts, drinking water, or skills like 30min seals as ret.
As for WSAD, i got my stun binded to S, but u can leave backpeddaling to S, although as ret i've didn't need it anyomre in pve or pvp.
Keep your attacks closest to you, often used spells like heal or hands spells in good position. Playing both 2v2 and 3v3, I tend to use modifiers on many skills, having shift for dps and ctrl for healer. Like key "X" for freedom, shift X freedom dps, ctrl X freedom healer. Same with HoP, Sacrficie or WoG.
CC can be u have similiar -I use shift modifier for focus stun/rep/rebuke. Actually using rebuke as C key = interrupt is most time-reaction demadning key to use.
Have a good luck in your road from Challenger ret to gladiator one. 80% is how good u are at controlling your character.