The spuds are super easy. No dimpling is needed. Drilling the hole was more of a pain for me than the soldering. I've had more trouble installing weldless kits.
To prepare for soldering, simply wind the Stay Brite around the boss of the spud overlapping on each turn, like a clock spring. Wind all the way to the edge of the flange. You basically want solder fully covering the back face of the spud where it contacts the outer tank wall.
Liberally apply the flux on all surfaces you want the solder to stick to. (This stuff is pretty strong. Wear proper PPE. You may notice it bubbling/fizzing.)
With the hole in the vessel facing up, rest the spud in the hole, with the solder sandwiched in between. Gravity is all you need... nothing else is needed to keep it in place.
Light your torch and start heating. You mostly want to heat from the top, and mostly on the spud... but really just keep the torch moving. Don't overthink it. The flux will boil and turn black and then magically the solder will melt and the spud will sink down nicely on to the vessel. Don't over do it. Once it sweats all around you are pretty much done.
After it cools down you will be ecstatic once you see how nice the bead fillet is on the inside.
1. You'll be good with the regular Stay Brite. The flux+solder kit is more than enough for your homebrew projects. I'm pretty sure it's 1/16.
2. I had the same issue with the bolt. I wish I ordered it from McMaster when I ordered the tool parts. I figured I'd go to HD and get one. FAIL. That and my issue with too large & too small couplers is why I abandoned the dimpling method at this time and went with spuds.
3. Not sure on the 1/4" spud but you are pretty much in drill bit range on that, so I'd just get the spud in hand and select the smallest bit that exceeds the OD of the boss.