A bulkead fitting is just the threaded fitting that has a jamb-nut on each side of the steel wall you are mounting the coil in.
Galvanized pipe is usually not great quality, the glavanizing ads yet another dissimilar metal to the system which with the water can cause galvanic action [corrosion] there is nothing wrong with all copper. It is the best in my opinion. [take that for what it's worth
For the support, I was thinking of only drilling two holes for the all thread, keep the pipe inside. So two 38" or 1/2" holes should not be a big deal, if you don't use them later, just put a bolt and nut in the hole.
As for the boiler's mass, well 10 gallons isn't much, so I guess a bigger tanks is in order. Is the basement a living space, like a bedroom? Or is it an 'occasional use' space?? The reason I ask is if you need to 'dump' excess heat, then just circulate the water in the basement baseboard loop, and let the rooms get toasty warm.
Baseboard needs fairly hot water to be effective, in my house, I can get away with 140-150* water untill the outside temps drop to the teens, then I need to have hotter water in the baseboards. Most gas or oil boilers are rated at 180-200* water. The hotter the water in the baseboard the more BTU's it can tranfer to the fins and air.
What I'm getting at is if your coil in the stove isn't able to create water hotter that 140* or so, then your augmented heat to the baseboards won't be very effective. However, a constantly circulating 110-120* is still going to create a lot of warmth.
I think you may want to plumb this system with a small storage tank, maybe use a used electric hot water heater tank, [usually free]. Just include shut off valves at strategic locations so you can bypass the tank [experiment #1], use the tank as a storage device for baseboard heat [experiment #2] and then plumb it in as preheated water supply for your domestic hot water [experiment #3].
Looking forward the the results of the experiments!!