I'm not MB, of course, but I also use a long hive (horizontal lang). Here's my $0.02.
Yes, use a follower. You always need to reduce the amount of empty space left to the bees.
I don't use a bottom board at all, instead I just have #8 hardware cloth stapled to the bottom. The hive is elevated on two concrete blocks but the screen is open to the ground and the entrance is via drilled holes in the front of the hive (or top entrance via migratories). I find this helps with varroa (when they drop out they drop aaaaall the way out), and I can get away with it because we have very mild winters. You could build a standard bottom board if you wanted.
You're right about supers, but make sure you have calculated the length of your hive correctly! If you're building it by assembling Lang boxes together, no problem. But if you are building from scratch make sure the length is a whole multiple of the width of the tops/supers you are using. Otherwise you may find yourself needing 2.5 tops to cover and having to fill the gap with plywood (works but doesn't look so stylish).