I prefer 645 for printing onto 12x16, because that way I frame the image in camera as I want it on paper, and I do not have to be aware of where I am going to crop. I would think 6x7 is a good format to use for 8x10 and 11x14. 35mm is the odd size that fits onto nothing except 4x6 postcards. As for ADOX 20 - I do not think the film is the only thing to worry about: There is also your camera's optics, the enlarger's optics, and your handling of both. It would take superb optics and technique to get more than what something like Acros 100 or TMax 100 can give for fairly little trouble. Then I'd rather just get a Pentax 6x7 with TMax 400 or whatever other film suits you. If I had the money I'd get a Mamiya 7 II rangefinder - there is nothing better in medium format, but the lenses are very expensive and the variety limited. I'll take the MF lenses any time of the day over the 35mm ones, to be honest. Only you can figure out what you do most, whether it requires you to be inconspicuous, whether you want to travel light, etc. Large format is a different ballgame. It is suited to studio and landscape where you have time to set up, focus, insert the film holder, remove dark slide, and so on, but very difficult to use for any action etc. Six frames would be a good trip. The ability to tilt and shift is a massive advantage for landscapers, though. Also, individual frame development can be useful in some cases. Per shot, it is five times more expensive than 6x7, and very time consuming, but the quality can be breathtaking. Is it quality or convenience or compromise that you want?
Yes, do use hypoclear. As for fixer, rapid fixer is fine unless you have a problem with the odour. My literature (multiple sources) states that neutral or alkaline fixer requires less washing than acid fixer, and I doubt that is based on hearsay alone. Even so, using hypoclear reduces the washing issue to a rather trivial one. If you can, use a two-bath fix and avoid over-fixing as that makes it more difficult to get the stuff out of the paper and may actually cause a slight amount of image degradation too. That said, not all can afford the space for a six tray wet train for 12x16 paper - I certainly can't and I have to adapt my workflow accordingly.