Airframe finishing and tooling

Hello again and thanks to everyone who gave suggestions on my search
for which aircraft to build. My shop is ready and I'm buying materials
this week to kick things off.
I've got some questions on how to properly prepare and work with the
aluminum I use in constructing my plane.

First: I know I need to sand/finish the cuts and holes I make on the
6061-T6 stock I use. The question is to what level. I know rough edges
are points of stress and should be removed. The question is what is
considered "rough?"
Like to what grit size sandpaper to work my way up to? Steel wool at
the end? I ask because the thousands of tiny scratches that even fine
sandpaper leaves could still be called a rough edge in some context.
Second: From what I read - the aluminum I use will be anodized which is
a process I know a little about - enough to know that any place it gets
drilled or cut will leave an un-anodized surface exposed to the
elements. What is the "Proper" way to protect these places?

If it matters - my plane will be stored in North Florida approximately
20 miles from the ocean so there won't be constant salt-spray involved,
but I do envision flights along the beach etc and I also have a large
fresh-water lake near my house that would make a great airport for my
eventually pontoon-equipped plane.

Lastly: What is the 'ideal' 3/8" drill bit and cutting lube to use for
drilling 6061-T6 in .125" plate and 2" square x .125" tubing? There are
only a few sizes that I'll be using on this project so I'm interested
in a "cost is no object" brand/type that would be best.