Probably regret this but here's my 2 cents

"Is trying to foil in marginal conditions likely to bring me more satisfaction of more frustration? :-)" - Foiling in marginal conditions is 100% more satisfying than fin.
I'm lucky enough to live 5 mins from a small estuary on one side and open sea on the other so foiling has at least tripled my sailing time in the last couple of years and the little refinements in technique and on water time have also helped my fin sailing for the wave days.
For the kit side unfortunately the old "buy cheap, buy twice" saying applies here, figure out what you really think you'll get most use out of first and then see what you can get it for.
From my experience, 95kg, 30+yrs windsurfing, pretty good level foiling 3 yrs now.
Get a foil specific board from the beginning,
If you're leaning more towards the playing around, gybes, tricks style of sailing then the Slingshot, twin track style of board is the way to go, something in the 100 - 115ltrs, 65cm - 70cm wide range should suit your size.
If you are looking for more of a cruising, blasting, speed sort of feel then the F4, Starboard Freeride etc with a board in the 120ish ltr, 80ish cm wide range is the way to go. If you go for this a 7m freeride / twin cam sail will add a lot to your range.
I started with the Gecko 133 so I could have the option to fin, never stuck a fin in it once, but did the job fine for the first year. Started with the Fanatic H9 foil, nice and cheap and did the job, but just not stiff enough, so plateaued pretty early.
Took the plunge and went to full carbon AFS Wind 95, game changer, and then followed with the JP Hydro 135. Have used this combo and 3 front wings with everything from 7.7 twin cam to 4.2 wave sails and rarely bother with a fin on flat water any more. Still nothing beats a good wave session though. At the lower end the difference in wind needed for a 5.8 Vs the 7.7 is really only a couple of knots and the choice depends more on the type of sailing I want to do, cruising or playing.
Have just got a second foil board, Fanatic Stingray 115ltd, and flow 3.0 foil set for more play around free foil, small swell light wind fun and might even try a wing.
On the speed side of things again it comes down to kit and ability, with the set up above, 22 - 25knts is comfy, 27knts is my peak with a 6.2 twin cam. Can always stay ahead of the local free riders until they're getting into well powered on 7m wind range.
And finally for the gybes, learning them was all part, if your base technique on the fin is ok and the kit set up is ok you'll pick them up quick enough, what I have found with foiling is rather than a full re-learning it puts a spotlight on any cracks. Biggest thing to get used to is the back winding mid gybe from the apparent wind, Took about 20 sessions to get the gybe started and as soon as I switched to the AFS it was waaaaay easier!
With sub 6m no cam sails I tend to go for the rig flip first, with the bigger cammed sails I tend to go for the step first to have a little more control over the rig, couple of little clips I put together below.
Anyway from the thread it seems like you're pretty much sold on the foiling so just enjoy