Sounds like you have the right ideas.
Personally I don't like the Weller wheels, but take a look at the repro Dunlop D1's. They do look fantastic and are real period wheels.
If it were mine I would get the corrosion sorted out, then go through it bit-by-bit to make it a classic car to be proud of. There a lot of period parts available on various sites. The original interiors from that time are classic in their own way and I would certainly retain that, although I might well fit better front seats. I would certainly make up an auxiliary instrument panel with a tacho and voltmeter and, probably, a clock.
A nice pair of period driving lights would look good. A good set of dampers and accurately set suspension will make it good to drive.
I would avoid wheel arch extensions if possible as they just attract more corrosion of the wheel arches and the chrome trims as original do look good.
As for body colour scheme I have always fancied a metallic ruby-red (nightfire red?) with a gold roof, but I have never done one that colour (yet). But I guess that wouldn't match the 1970's interior maybe.
A period-modified Mini will be very nice to drive, attractive when taken to Mini shows and will have an excellent retail value increasing over time.
But that's just my take on it.