Since 4.2 is the highest available update, you will have 4.2 or lower. I was about to say, look for yourself if the HBC is installable on 4.2, but then i saw that it's not stated there. At least not directly. Anyways, on 4.2 you can still use bannerbomb(that's required to install the HBC) to run the hackmii installer(which installs the HBC).
(most likely) indeed. But you can still set up a USB hard drive full of games and play your wii games from there. So aside from a faster loading time, not having to actually switch discs and not run the risk of burning a few wrong discs, things aren't so different.
(and it's not like those differences are actually a disadvantage
Besides...in your opening post, you mentioned you most wanted to have the HBC. You can have that. And pretty much all the homebrew you can handle.
Oh, and I might be wrong, but according to this table, uloader has the option to "start game discs from external USB DVD reader". Perhaps that's worth checking out.