Most of the important points have already been covered, but I will reiterate and add a slight bit.
When you buy the press, make sure you get the "Classic" version with the low flat cast iron base, not the slightly cheaper version with the raised aluminum base.
Any dies that work on your RCBS press will work just fine on the Lee Turret press, but you MAY have clearance problems with some lock rings. I use some Lyman dies with their stock split lock rings on mine with no problems. But I prefer to use Lee dies.
You do NOT need to use the Lee Factory Crimp Die - in fact, I strongly recommend against it unless you have a specific issue you need to solve. IMHO, the standard seating/crimping die is ALWAYS the better choice. Some people will disagree.
Shell holders are interchangeable in all standard presses, just note that each manufacturer uses different numbers, so you have to have a cross-reference if you use more than one brand. If you buy new Lee dies, they come with a new shell holder, too. I personally like to have a second set of dies - I keep the Lee dies locked in the turrets, and I use Lyman dies with split lock rings to easily spin in and out on my single stage Rock Chucker press when I have small batches to load or need to just do one thing.
If you are going to use the press with auto indexing to load sequentially, you really will want to get a Lee powder-through expander die and one of Lee's auto powder measures - do go for the new auto drum. Although the older auto disk measures work fine, the new drum measure is about the same cost and is just a better idea. You have a choice to buy either a new set of Lee dies, which are much less expensive than other brands, or just buy the expander die and use it with your existing sizer and seating/crimping dies.
The Lee turrets are 4-hole turrets, which means you will be left with an open spot if you load with just a standard 3-die set. You can use that open position to add a powder-cop die if you like, or do as I do - just manually move the turret one position as you add the next empty case. This takes virtually no extra effort and becomes second nature real fast. Just remember, you MUST NOT try to move the turret by hand with the handle either at top or bottom of the stroke or you will bust the little plastic doohickey that rides on the actuator rod to automatically turn the turret. Here is the correct process: Slip in the new shell right after you remove the finished round, then begin raising the ram while you reach up to touch the turret - when the ram has come up about one inch, the turret is free to move, and you can advance it to the resizing die easily before the new shell reaches the top.
If you want to come over and visit the Sacramento Mountains, give me a shout - I'd be happy to show you the process I use with the different presses.