You should be fine. Mason bees don't travel as far as honeybees in search of pollen, but they do make the rounds within a neighborhood. I have never utilized mason bees but there certainly seems to be enough pollinators around, as my tree produces well each season......sometimes too well :-)

All apple varieties have the ability to get large, however you will almost always find them grafted onto dwarfing rootstock. A semi-dwarf or dwarf tree should remain a good size for an urban garden. I'd avoid a minidwarf, as there is too much incompatibility with the rootstock and these little tiny guys often fail.