Well you could ditch the adapters and order the axles at 4.5 (or have your stock ones re drilled) or keep the 5x4. Either way this will reduce your backspacing and should make your wheel choice a little cheaper.
Take stick and lay it across the rim (laying on the rim lip/edge) then take ruler/tape measure and measure the distance between the hub and the stick. That is your backspacing of the rim.
To do the wheel well its the same basically. A stick from the axle hub to the top of the wheel well then...
It helps if you state the car the 8.25 rear is going into. I mean your avatar shows a 64-66 barracuda but you could be sticking it in a dart or duster etc.
Great question why make two different bolt patterns on the cars. It's cheaper to make one size bolt pattern and wheel selection is basically the same. Whatever?
If you want any type of real performance tire you need at least 17" however I have noticed the most size with widest selection of performance tires is in 18"
Also know that for every 1" in rim diameter you lose 1/2" on sidewall.
4"=101.6mm good luck finding wheels in that pattern.
4.5"=114.3 you can find wheels in this pattern any day of the week, in fact you have wheel option overload.
215/225=tire width in mm, 60/70=percentage of tire width in the side wall, 14/15=wheel size, and R=radial.
So yes assume the same tire width, the 70 will be taller then the 60.
When I put a car up for winter or just storage, I put it on jack stands and drop the air pressure on the tires to just 20 pounds. Less stress on the tire and won't leave flat spots. In your case I'd put it in a corner and call it good.
There is a more tire options out there, then what you just listed. Example my old 85 GP had Toyos 225(could've been 235)/50R15 at all four corners and I had no complains what so ever on those tires. Those tires made a really cool sound when I would get on the I-5 and it was wet! Sounded like a...