If you go for one of the kits, whether RCBS or Lee anniversary or whatever, they have most of the tools you'll need. I don't know whether the RCBS has one or not, but a case trimmer will become necessary eventually; they're $3-$4 for the Lee version, but you need one for each caliber you're loading. Also a chamfering/deburring tool.
All kits I'm aware of come with powder scales; if not, get one.
I prefer a Lee hand primer, but I'm not using a press at the moment anyway; I'm using the Lee loaders. In which case I also use a couple of hammers :shock:
Among the things you need that may not be in the kits are:
A good caliper for case & OAL measurements. The digital ones run close to $40 most places and are easier to read than the dials; I found one at Harbor Freight Tools for $16 on sale.
Some kind of shell holder when you're working with 100 or more rounds at a time. You can lube them all at once that way if you're using a spray lube like One Shot, which is what I prefer.
Scale check weights. You need to check your scale with known weights periodically to make sure it's accurate/calibrated.
A Chronograph. $100 or so new; I'm looking for a refurbished one but haven't found one. Since a home relaoder has no way of accurately measuring pressures, a chrony is the next best thing when you're working up to max. loads.
Several manuals. The Lyman 48th edition has helped me greatly, and I picked up some of the "One Book/One Caliber" manuals for each caliber I'm loading; they have advice from each bullet & powder mfg. for the caliber of your choice. There are others; read as much as you can and educate yourself.
This and other forums have lots of experience you can learn from. Be careful taking maximum load advice from anyone; always start with minimum and work up to it from there.
Every time you change a component in a load you like, such as bullet type or weight, start back at minimum. Things can behave very differently with minor changes. Also, be aware whether a bullet or powder manufacturer you're using has changed things; that can alter the accuracy of a load a lot as well.
Lastly, be careful of the "I want all the velocity I can possibly get" mentality. It tends to lead to high pressures and dangerous loads for some people. A .223 shooting 50gr NBT's at 3250fps will kill a coyote just as dead as one running 3400fps, and may even be more accurate. Not everyone gets carried away doing this, but some do. Don't take chances. Do I sound paranoid? Let's just say I once had an eye-opening experience using black powder... :shock:
Good luck, and stay safe. Let us know what you decide...