I did hot salt bluing for quite a few years. I used a set up that was sold by Heatbath Corp. (they still sell chemicals) and used a Nickel Pentrate salt. I had tanks set up in one stall of a 2 stall garage and it worked fine. It consisted of 3 tanks and 2 burners and all the equipment needed to do high quality hot blue/black except for the fuel. I used 20 lb propane bottles for fuel and got a couple of sessions from 1 bottle. I only blued a few times per year and always had a waiting list for when I did blue. Just amazing at how many friends you acquire when you do hot bluing...
I had a couple of extra tanks welded up but never finished the legs. Everything sits clean and dry in my shed waiting for me to get motivated to offer them for sale. This set up can be used with any of the salts sold by Brownells or other chemical distributors. If you ever get to upstate NY (150 miles north of NYC) and think you might be interested in this I'll give you the $.50 tour and a deal...
An important consideration is protective clothing, it is a must have. One time when I was cleaning up at the end of a session, (tanks were cold) I had an itch on my cheek and brushed it with the back of my heavy rubber gloved hand. I didn't realize it at the time but I had deposited a minute amount of dried salt on my cheek. About 2 hours later after a shower I noticed that I had a tiny burn on my cheek where the salt was. Took a long time to heal but it did.
The bluing of steel is pretty easy and straight forward. It is the polishing that is where the real work is. You'll need buffing wheels, (both loose and sewn), polishing compounds, a very fine wire wheel. It takes some practice to not polish down or wear away the stamping on the firearm, (you should practice on some old clunkers) IMO that is what makes a good job. To make a re-blue look like original or better is what I was after. Some firearms had 2 or 3 different surface finishes and in most cases I strived to duplicate those finishes. I suppose it could be considered restoration work. It also depends on what the customer wanted. I had a lot fun and met some crazy people...
If you didn't know, anything with barrels soldered together will have to be cold rust blued. Bluing temps are high enough to melt solder and that prized s/s is not a s/s anymore... No brass or lead goes into the tanks, It will ruin the salt solution.
Sorry I was so long winded here and didn't address your question. Feel free to pm me if you have any questions.