The ABC's of Reloading is a good place to start.
.38 special and .45 acp are about as easy to load as they come. Both are low pressure loads. When shooting .38 specials in a .357 magnum pistol, the safety factor improves. I think loading for .38 special would be the easiest to load. You do have to make certain you don't double charge the load. It is a big case. At the moment small pistol primers are in short supply at the moment. Large pistol primers are normally used, but not always, in .45 cases. They can still be found fairly easily at the moment. Later in the year the primer shortage will probably go away. Now is still a good time to start reading up on the subject.
9 mm is the cheapest caliber to purchase in center fire factory ammo. At the moment it is in short supply. What there is available seems to be rather high priced compared to just a few months ago.