Heat treating 4140 at home can be done, but you need to learn your forge/furnace first. I'd recommend a good infrared forge thermometer so you can get a feel for temps inside while you're running it.

You need to soak the parts at temp for about thirty minutes per inch of thickness, which means you are going to need to keep that temp pretty steady. You can't just crank the propane to max, make the part glow red, quench, and be done in 10 minutes. You have to heat up over time, uneven heat can cause internal stress and warping, hold it relatively stable at ~1550-1600 for at least half an hour, quench it to ~150, and then proceed directly to the tempering oven and hold it for the same 30 minutes per inch of thickness.

Your tempering temperature will vary depending on what hardness you're shooting for and what yield strength you need to keep your chambers from deforming, this is critical "you will get a face full of shrapnel if you fuck it up" information so I leave that up to you.

There's a couple people on the singleactions forum that have done custom revolver cylinders and documented their projects, so I can say you're definitely on the right track and your goal can be done. You just need to do a little math and make your own safety calls for wall thickness and tempered hardness because there is no one single answer.