That's looking great! Is it mild steel? The black coating will probably wear off eventually. Mail tends to de-rust itself this way, so the coating will do the same, I hate to say. But depending on how they did it, it may remain a relatively dark color anyway, and may last a long time.
For oiling, you might consider spray-on gun oil. I haven't tried it yet, so take this with a grain of salt (most of my mail is aluminum or stainless).
I haven't tried a vacuum bag. Cool idea though.
As for the baggy sleeves, you can probably alleviate some of that just by running some laces through the mail to tie it down to your arm in several places. It takes longer to put it on, but since it's not ridiculously wide (like the "wings of mail" that you can get with a lot of other off-the-shelf mail), you can probably get close to a tailored look this way. They gave you enough length in the sleeves that once it's tied up, it'll come back behind your wrist and won't look too long.
How's the fit below the waist? Any trouble sitting down?
