I'll let others cover the suppliers, since I have a good local and don't mail order much.
For a .45acp, make sure your cases are clean. You don't need to tumble them every time, just when they are getting a bit grungy. Too much dirt too often can mess with your dies over time. Visually inspect each case to make sure there is no tumbling media inside. This reduces case capacity and has a much more pronounced effect than in larger capacity rifle cases.
Buy carbide dies, if you don't have them already. This eliminates case lube.
Shoot lead if you can find it. It's usually much cheaper than jacketed and works just fine. *Charge weights are different from lead to jacketed bullets* Use the correct load data.
Keep things a bit on the long side. Stick with as close to 230gr bullets as you can get, load them to max OAL, which should be magazine length. This is not true if using a wadcutter bullet, but i usually use conical lead.
Put a good crimp on the case. The crimp is different than the usual roll crimp used in most rifle cartridges. Pistol rounds use a taper crimp, a slight squeeze at the case mouth. Even with a cannelured bullet (not usual in .45 loads) there is just the slight taper crimp.
Use a powder that will not permit a double charge. If a double charge will physically fit into the case, choose another powder. Reloading the massive quantities involved in most handgun operations needs a few built in failsafes. Eliminate the double charge possibility.
