Mcmaster is a bit too pricy for plain old fittings but if you're already ordering from them for some other reason, go for it.
Buyfittingsonline.com is by far the cheapest. I'd recommend 1/2" full couplings for the bulkhead and then you'd want to look at what thermometer and/or sight glasses you might want require. By far the most common thermometer thread is 1/2" but there are others out there. If you used my sight glass, right now it would be 1/4" thread.
I wouldn't JB weld. I'd use a weldless setup before I did that. If you have a propane torch you can thread a MAPP gas tank on and pick up a silver solder kit (not at lowes or depot). It's not hard to do but if it's your first time soldering anything, it might be a little intimidating.