617 fan, yes to everything that has been said above, however, lets not over complicate what isn't all that complicated. You want to start reloading for 3 guns in .38 &.357? I would suggest that you buy a good reloading manual I would suggest Lyman, but there are many good ones, you only need one to start, but read it thoroughly. Then you will need equipment, Lee is exceptionally inexpensive and plenty good, however RCBS, Lyman and others offer kits, get one with "everything you need" to get started.
Having read the manual will let you know what it is that you need to get started, I won't list them the manual will have done a better job than I can. Then decide what you want to do and buy components accordingly. For example if you want plinking rounds in .38 special and Hunting rounds in .357, yo would need at least two different bullets as good hunting bullets are rather expensive for plinking and plinking bullets may not be optimum for hunting. Yo already appear to have brass for both .38 and .357, so primers, I would avoid all questions of mag and standard small pistol and just buy small pistol, Winchester, CCI or Federal even Wolf if you can find them, all are fine. Then powders, not too hard, you could buy one medium powder such as Unique or Power Pistol and shoot small amounts in the plinking loads, but I wouldn't. If I wanted to plink I'd buy one of the faster powders, Bullseye, TiteGroup, etc, but here is where the Lyman manual comes in handy. Lets say you bought 158 gr LSWCs for plinking just look in the manual for the suggested powders (Lyman will even suggest a most accurate load) and pick a powder that works, I'd suggest one that has wide application because you probably won't stick to a single plinking bullet but will want to try wad-cutters, plated bullets, etc. Then go to the recipes for the .357 hunting bullet you bought and pick a powder to buy that works well, i.e. gives one of the higher FPS but does not require mag primers, 2400 is a real winner in .357, but there are other good choices like AA#5 or #7, etc.
So you will have purchased a manual and read it pretty much cover to cover. Yo know know enough to pick the rest of your equipment and supplies to load to your hearts content.
I started much this way with a Speer Manual, A Lyman kit, and a pound of Bullseye and eventually added Unique as I became more power hungry. Best of luck, I hope you enjoy reloading, by the way that 2lbs of powder should be enough to load over 2,000 rounds!