X-PRO1 and X-E1 have first gen sensor that was improved in many aspects for x-E2 and X-T1 (and now X-T10); X-E1 also has an electronic viewfinder that is so slow that you'll be anticipating all photos you're gonna take; X-PRO1 used is ridiculously expensive. In brief: don't buy them.
You can go for X-E2 that is good overall.
In my opinion X-T1 is very good but still lacks important features that I want for it's price.
Better buying a X-T10.
If you want to go for something useful and cheap go buy a used X-E2.
