Help Needed! Tire Sizing Question

[Prestovie]

Hey guys, I don't get on this forum nearly enough(spend a lot of time on ZHPmafia lol) but I'm coming here to ask for some help regarding an e30 project I'm about to be getting into.
In the next few months I'll be purchasing an e30, most likely a 1986 325e or a 1991 325i. I'm going to need to get it before the summer so I can take it up to work which is about 5hrs into Wisconsin, and I'll be driving a lot of dirt ad gravel roads(hence the reason the I'll be leaving my ZHP behind). So I was watching some videos on people having a lot of success with BF Goodrich All Terrains, and I'd be all for getting a set of those, but I have no idea what dimensions I need to be looking for. The OEM wheels are 14" but apparently they don't come in that size, so if I were to buy 15" what size should I look for?
I'd be all for cutting some fenders and putting flares on just to fit them. Does anyone have any experience with this type of thing? Like if I went with 15" or 16" wheels does anyone have recommendations for which wheels I could buy cheaply used?
I know it's a lot of questions but I'm just trying to get everything mapped out that I can
Thanks guys

[MIKYZZ4]

(86 325e)(91 325i)205-55-15,205-50-16,205-45-17,215-35-18
Verify with TireRack optional wheel size selector.

[Prestovie]

(86 325e)(91 325i)205-55-15,205-50-16,205-45-17,215-35-18
Verify with TireRack optional wheel size selector.

Thank you so much!

[Jim@tirerack]

You would have to do more than fender modification to make the BFG All Terrains fit. They are really tall so you would also have to lift the car. There will be no AT type tires that will be an easy fit on your car.