OK first, beware of your lead source. For round ball, you want as close to pure lead as possible, because the molds are made for that, and because you swage a revolver bullet into the cylinder (as I'm sure you know) and alloys a) don't shrink as much when they cool so can cause problems with patched round ball in rifles, and b) are harder when trying to use them in revolvers, and c) when cutting off the sprue, the extra lead formed above the ball when the bullet is cast..., some alloys make that cutting very hard to do and hard on molds. So don't take the local scrap dealer's word for anything..., check any and all lead that you get. It doesn't take much tin or antimony mixed with your lead to get it harder than you wish.
IF you do end up with a bunch of alloy don't fret. You can soften it a bit by mixing it with pure lead, AND you can use it to shoot patched round ball, you just have to work up a load with a thinner patch OR get a mold that is small, say like .005 smaller. I know of several fellows who use alloyed lead for patched round ball. They have access to recovered handgun slugs, which are pretty hard, but they work fine on deer and on paper.., one fellow uses a thinner patch, and another uses a smaller mold.
Lyman or other steel molds are by far the best..., but they cost more than 2X what the Lee molds cost. While Lee molds work well, they are aluminum, so you must read the directions that come with them, AND treat them gently. One common mistake is when preheating the aluminum molds folks sometimes heat them open, instead of in the closed position. Uneven heating of the two sides can cause problems with casting and wear them out fast.
Bag molds are the ones that you see that look like a pair of steel pliers. They were the original DIY mold for the rifleman or the pistolero. You use a very small iron pot or just melt the lead in the ladle, and pour one or two balls from that lead. They are good molds once you learn to use them, but you cut the sprue after you let the ball completely cool, not when opening the mold as you do with the modern molds. The handles can get pretty warm with a bag mold too. I do a lot of bag-mold bullets for my traditional black powder rifles, and muskets, but I'm also at historic sites doing bullet casting as a demonstration for the tourists..., and plugging in a lead melting pot just won't do.
Casting machines are great, and save a lot of time. The basic ones are merely electric melting pots. Some of the basic ones act as a ladle, and some you dip from with a ladle. They aren't too expensive AND they have thermostats so when you get the lead to the right temperature, they hold it there (using a fire and a kettle and a bag mold in the old-time way, the lead temp varies, and you can get wrinkled balls or frosted balls
) Basic electric lead melting pots are ok for pouring a dozen round ball, but if you're doing a huge batch as one often does for handguns, especially when using a gang-mold (makes more than two bullets at a time) ..., the basic electric lead pot may hold too little lead. The standing, bottom pour styles tend to hold a lot more lead, AND are much simpler to use, though the cost goes up a little, or a lot if you buy a large model. They tend to be more convenient, especially if you need only to use pure lead or one, simple mixture for the alloy of your choice.
I hope this helps to answer your questions.
LD