Welcome to the wonderful, oft confusing and frustrating world of reloading.
First; reloading manuals are not hard and fast formula. They are published reports of what some test techs found when they used their components, in their equipment with the listed amounts. Bullet manufacturer's will use their bullets (of course) and their manuals are good in you choose their bullets/components. If you chooseHornady bullets, use Hornady data. After you get the basics and theory of reloading down, you can extrapolate load data from one bullet manufacturer to another if the bullet is the same weight and shape.
Mixed headstamps for reloads is no problem, and the only time I sort my handgun brass is when I'm working up a specific load or I'm realllly bored. Yes, the internal dimensions of cases can vary, but for new reloaders using book loads there is not a problem. If upper loads and deep seating bullets, then perhaps there could be pressure problems. My suggestion is to find a load in your manual(s), then buy components, start with minumum listed loads, use listed dimensions (OAL).
I do sort my brass (actually unnecessarily) for my "special" loads, for my heavy 44 Magnum loads I use the same brass each time. For my "accurate" loads I usually keep the load to one manufacture of brass, but that's just me and my OCD.
Go slow. Double check everything. And most important, have fun...
FWIW, prolly the easiest, most forgiving round to reload is the 38 Special. As long as the load is safe and your reloads fit the cylinder, you're good to go. Reloading revolver ammo is simpler than semi-auto because as long as the cartridge goes into the cylinder, quite easy to achieve, it'll work, but semi-auto ammo needs to be able to feed and chamber and cycle the action. Seat bullets to the crimp groove for your revolver and forget measuring length. I started reloading in '69 with a Lee Loader in 38 Special with Lee's instruction sheet and successfully loaded for about a year before I got more "sophisticated"...