Great job, there. It's always fun to "tinker" in the shop.
A little note for those who do not have access to a welder. Use standard plumbing pipe pieces. Bolt a pipe flange to the bottom of your new forge (a flat round plate that allows you to screw a threaded pipe into it, and bolt it to the floor or wall). Then screw in a section of threaded pipe. Then thread on a T joint or coupling, with the leg of the T sticking out to the side. Attach a short section of pipe into that joint sticking out 90 degrees. You attach your blower to it. Then thread in a short section of pipe into the other part and another pipe flange onto it. You can then bolt on a flat iron plate to that flange so that you can swing it open or shut - this is your Ash Dump. That whole bottom assembly can be made out of those pipe pieces - and without any welding. 2 pipe flanges, one T joint/coupling, and three short lengths of pipe threaded at both ends is all you need. With a couple bolts to attach it to the bottom of your forge, of course.
I've lived without a welder for many years, so I'm always looking for ways to do things without using a welder, or having to drag stuff over to a friend's house for him to do it. One of these days I'll get a MIG welder, but not just yet.
Another simple, but potentially dangerous way to cut those tanks apart is to use a "poor man's chop saw". Get a metal cutting blade for your circular saw (skil saw). Hold your tank securely on a low bench. Put on all the safety gear you can think of - boots, coveralls, face shield, heavy leather gloves. Place the front edge of the skid plate on your circular saw against your tank, and then slowly tilt that spinning blade down until it starts cutting/grinding through your tank. Hold it tight with a firm grip! Cut in a ways, then move the saw or tank a bit and cut a little more. DON'T RUSH IT! GO SLOW! Let the blade do the work. To me, it goes better than using the angle grinder to cut. I've done both, but prefer the circular saw when I can get in and use it. Of course, I also use a wood blade in my circular saw to do some free-hand wood sculpture. My buddy Otto can't even bare to watch when I'm doing that. He has the local rescue unit on speed-dail whenever he's around me. (Never had to call them for me yet! Altho, he tends to cut himself most every time he picks up a knife.)
Just some humble thoughts to share. How you use them is totally your own responsibility.
Note: your buddy's will remember every little "mishap", and remind you of them FOREVER. They may not remember what they did with the tools they were using 10 minutes ago, but will have all of those little "incidents" firmly locked into their memory. Nothing helps keep you humble like your buddy's memory.
Mike Ameling