will there be any additional wear on the chain and chainrings from using my legs a lot? so many variables...
Not really - you spend so little time braking compared with pushing forwards, and the reversed load is wearing a different part of the chainring and sprocket teeth anyway.
Probably, although disc brakes are the way to go if you're wearing rims out quickly. If you stick with rim brakes, ceramic coated rims are probably worthwhile even if you do your own wheel building and cost it at zero, if you're paying somebody else to do it then definitely go ceramic, e.g. http://www.sjscycles.co.uk/rigida-grizzly-700c-(622)-touring-rim-with-css-side-wall-black-prod18886/
Not really - you spend so little time braking compared with pushing forwards, and the reversed load is wearing a different part of the chainring and sprocket teeth anyway.