Nice Work McRaigl. Must be really nice to have access expert instruction like Mike-HR close by not to mention access to a power hammer
As far as tips on polishing go, those mini flap discs for the Dremmel or Roto zip are expensive compared to the flapdiscs for a 4" angle grinder, not to mention the 4" grinder has way more motor to get the job done faster. I'm guessing you dont have a one of those yet, I'd suggest buying a good one like a Milwaukee or Dewalt, not the $19.00 H.F. Chinese model , but even the H.F. one should last a good while if your not running it 4-6 hrs a day 5 days a week. Or like you said the pneumatic Die grinder might be a good option, if you already have the air compressor. I use lots of those 3M Rollock Discs, ( looks kinda like a scotch brite pad ) for odd shaped surfaces, so your on the right track there. Just use something to knock the scale off like an overnight soak in some vinegar. Forge scale eats abrasives faster than hardend steel some times.
Personally anything past about 400 grit is HARD WORK ! IMHO, I usually don't use a buffer on my blades so a hand rubbed 600 grit finish is sort of my standard, either that or a 1000 grit waterstone finish with a light vinegar etch. I just don't have the patience for mirror polishing
To keep rust away I use camellia oil or marvel mystery oil.
Hope this Helps ,
Jens