I've never done a full sole swap before, so I'm not positive, but I think you should get the same size doner. I've reglued shoes with a shrunken midsole (because they were in a hot car) and it's a ***** to stretch it and make it fit.
Always get the same size.
Yes, just clean them with dish soap/detergent + warm water + toothbrush. Dirt is very easy to clean. I wouldn't worry about the oxidation/yellowing process to much, shoe will naturally yellow anyways. Just don't wet them and then put them on dirt again, wear them right after, etc. clean and them let them air dry.
From my knowledge and this may be outdated (and I could be wrong), but in the past, before the GM/UA craze, people just had regular rep jordans and the 23 was always messed up (extremely stretched/fake). So since the reps had poor screen printed "23's" on the back ,people would use acetone and just wipe it off and then iron a new 23 on there to make them look legit. The "23" on the legit pairs are actually good/better quality material and not like the poor screen printed material on the reps which is why I don't know if it will work, but pretty much as long as you can strip the "23" on the legit pairs, you can do the "fix."
Like stated already, all the answers to your questions have been posted in the last few pages...but I'll help spare you the work this time.
kintan
No, if you are going to do that you should use plastic because the cardboard moves around in your shoe and shreds into little pieces and it is hard to clean out. If you want sneaker shields, go to footlocker and buy them, they are about $10. Your shoe is going to crease anyway, so its pointless. Just wear them.
