1. Should do but peoples 3bet ranges arent wide enough in many full ring games - 6max different.
eg. some people still only 3bet AA/KK in full ring

2. No - ranges are much different

3. No good option - personal preference - probably some sort of check-raise repping better than Ax - but SPRs would be wrong and in small stakes games no one folds AK in 3bet pots on Axx (they probably dont higher up either)