12b is talking about loading blocks. Not indispensable they are both very useful and rather frustrating because of the "one size fits none so two sizes that fit none are better" aspect. Since you are going low cost/low tech you can be aware of the possibility of double-charging especially in pistol calibers and inspect the powder loads visually with a flashlight before pressing in the.bullets. Loading blocks/ trays help organize that and other procedures. You can make do with the primer feature of the press if it has one... but I really, really like using a hand primer. For that I like the RCBS APS strip loader and use one for each size primer so I don't have to change the "doohickey". Case trimmers are essential, but not to get started. You can wait a little while. Lee single stage presses are perfectly good at doing the job, the single stage is just more time consuming and musical-chairs-ish. I've got 3 or 4 of them, as well as Lee and RCBS turret presses.

I agree on loading the pistol rounds first...either the 9mm or the .45 ACP. If you get any small-primered .45 ACP, just throw the damn things in the trash brass bin. I keep what's left of a deprimer rod after the pin breaks off handy when prepping ,45 ACP brass. It will fit in to a large primer pocket but not into a small primer pocket, so... any .45 brass that is a no-go, is gone.