Oooh, ooohh!! Pick me, pick me!!! I've been doing it since about April of this year.
We actually purchased all our equipment and supplies, and most importantly got our training from TWN, the ones you've linked to.
I'm not 100% sure how much we're into it currently (my partner handles all the book keeping for that business) but I want to say it was somewhere between 8 and 10 grand to get us started, not including the space.
In addition to the tank (really not all that complicated. I think it was in the 6k range if memory serves) you'll need a
good spray gun to dedicate for the activator, a spray booth or other space to base paint & top coat your parts and another spray gun for that. A compressor (obviously), a cutting surface for your film, a rinse station for after you do the dipping, somewhere to hang & dry parts, and an airbrush for touchups.
Oh, and you're going to go through a
ton of masking tape.
There's a good bit of "science" & technology to it, but there's a lot of art in it as well. I would definitely suggest you go for the training if at all possible. It was well worth the money!
We are continually getting better at it of course, and I look back at some of the practice pieces I did when we were starting out and laugh at myself to be sure. It definitely takes a good bit of practice and it'll be a while before you're ready to sell the service. You have to be able to figure out the best angles to dip your piece so as to not trap air pockets and get complete coverage, but you also have to make sure that you don't let the water break the film before it covers the entire surface or you'll have voids in your prints. Many things can be done in 1 wrapped around dip with careful planning, but some of the extremely complex pieces have to be split into 2 or occasionally more dips. The majority of our work is firearms at this point, though we have done some fun stuff like SCUBA tanks, baseball bats & helmets, and even some juggling pins.
Hopefully this won't be considered self promotion,
(if so mods feel free to delete this part), but if you would like to see some of the stuff we've done, you can take a peek at our gallery here:
http://www.hydroprintservices.com/gallery.html
If you have any other specific questions, just ask away!