I moved from 3x24 1080p to 3x32 2k about a year ago (in fact to a 3x32 in the lower row and 2x32 in the upper row, mostly for work purposes) and no matter the size of the monitors VR allways win, with my pimax 5k+ i have huge fov but a bit of screendoor, my recently buyed quest 2, have so much smaller for but the image quality is impressive for a tiny-cheap-wireless HMD.
About the GPU raw power you need, there isnt a big diference from triples to VR.
About your last question... is not just the size of the screen setup, is the distance from the screens to your eyes, , to have the rigth size you need the screens really close and lowered to fit everything in the rigth place around the driving wheel and i dont know how old are you but since some years ago presbyopia comes into my life ( age is a bitch) and i cant put the screens closer like before or "human biological antialiasing" comes into the game and i save some GPU resources but its kinda painful after a while. When using VR i dont have any sigth issues related to presbyopia.
I dont know if you already tried VR before, or if you tried it with a WMR headset (poorly polished runtimes, bad performance, really hungry in GPU resources and bad tracking even if some have very good image quality), but if i was you i give a try to a quest 2 before build your new triple setup. If you like it but you miss some FOV, you can move to another headset with wider fov and still cheaper than a 3x32 setup.
I know ACC quality in VR kinda sucks, but with last patches even my gtx 1080 can move it with at least some decent image quality, far away from AC AMS2 but at least is playable, i suposse with better GPUs you can achieve better quality.
Regards.