... So without some experimenting, it'd be just buy everything. And if I believed everything I read I'd buy nothing...
... Where do you start and where do you stop. The line is pretty blurry in a thing as subjective as the proper way to do reloading...
777Funk, I've noticed that you've posted several questions regarding some of the basics of reloading, and I would encourage you to continue asking questions. I know it may seem overwhelming when you're just getting your feet wet. There are good-ways, bad-ways, no-ways, and all-ways that you need to carefully consider when making decisions about reloading. And, you're right; there are many, many different set-ups used by a very diverse bunch of folks. And, each of those individuals has some kind of opinion about what's best. But, in spite of the chatter about particular methods or equipment, there are some general guidelines that should always be followed.
Also, the equipment doesn't have to be expensive (I successfully made my first hand loads with a $15 Lee Loader I got at a pawn shop), but there are some pieces that are necessary. Likewise, which steps to take to end up with satisfactory ammunition, and the order in which those steps are taken are commonly debated on the interwebs. But, there are several steps that are necessary to end up with safe ammunition.
With this in mind, I would respectfully make a recommendation. Please, before attempting to load any more ammunition, read "The ABC's of Reloading", cover to cover, twice. And then go back and read it again. Then, refer to it regularly as you progress from step to step in the reloading process. I'm not kidding. That book covers a lot of information, and a quick skim will give you just enough information to be dangerous (as will asking random questions on internet forums). You not only need to understand the physical process of hand loading, you need to understand why you need to perform certain steps, and what can happen if you "do this" or "don't do that". Doing something "unconventional" may not necessarily be doing it "wrong", but you do need to understand the consequences of doing it a certain way.
Also, pick up a copy of the 49th edition of the Lyman Reloading Handbook. But, don't even look at the load data section in section 5 until you've read Sections 1 and 2, which cover Safety, and the Basics of Reloading. Lyman has been publishing this manual for a very long time, and they have a pretty good idea how to do it right.
And as you read these books, and start reloading again, keep asking questions along the way. As good as they are, there are certainly things that the books may not cover, like whether or not you can set the decapping pin in a full length sizer die so you can deprime before tumbling. In this case, the answer is "probably", depending on your particular setup. Of course, when you ask such a question, you have to expect some of the replies to be "
just buy X, because that's what I have, so it must be the best way to do it". It's kind of the nature of the beast.
And, one more thing regarding your original question about decapping dirty brass, I would recommend cleaning your dies afterward. I wouldn't want any grit floating around in the dies when I went to resize the tumbled brass later.