Hi Brian,
Unless you need a true motor drive you may want to consider getting a motor winder. For the R4-R7 you can use the motor winder R4 or the improved motor winder R. Selection of a motor winder instead of full motor for the R8 or R9 might also be considered.
As to SLR cameras unless you want the older SL/SL2 or R3/R3MOT series I would look at the R4s and later.
Generally, I would stay away from the R4. The R4SP is a different question, have one and really like it (had 2 sold one). This is a simplified version of the R4 has both simplified metering and better adjustment for Bracketing in Automatic. Has basic spot and averaging metering. Has 1/100 and B settings function without a battery.
Next and with more features is the R5- never owned one, but the first with TTL for flash.
Next automatic and last in the series is the R7. Like the R4s and R5 uses LEDs in the viewfinder but with much more information available. This is the first in and I believe the only camera in the series to have a special socket for mirror lock up. Has a newer and more flexible TTL metering. Paperweight without a battery. I have one and I like this as well.
R6 and R6.2 are the strictly Manual metering cameras of the series. Never owned them, but as I remember the R6.2 has a more sensitive metering. Cameras will function as I recall without batteries, but you have to confirm this.
Of the cameras above, all but the R7 are about the same size and weight and built on the same chassis (but heavily modified and improved) over the Minolta XD11. The R7 is built on the same chassis but is a little taller and heavier. There are some minor changes in the cameras going through the series.
The last 2 Leica R cameras are the R8 and R9. I have the R8. This and the R9 are different animals than the previous R4-R7. These were designed and manufactured in Germany and are a larger and heavier cameras. Both cameras can also take the extremely expensive Digital Module R for digital usage and require the removal of the film back and replacement with the Digital Module. These 2 cameras have tremendous amounts of information in the viewfinder and there are histogram type bar indicators indicating 1/2 stop increments away from proper exposure. These cameras have true mirror lock up, improved TTL, very high sync or 1/250 as I recall, improved metering, more metering patterns, 1st & 2nd curtains for flash.... They are paperweights without batteries.
The R8 is the slightly heavier of the 2 cameras and there are only minor improvement for the R9. In fact my friends at Leica Camera, USA said they did not feel I would benefit from getting an R9 and replacing my R8.
For me, the R8 is my favorite 35mm camera that I have ever used. If size and weight are not an issue, this is my camera of choice. If I need small size and weight are an issue, don't need TTL, and a camera to function without batteries the R4SP is my choice. If I need almost as small a package as the R4SP, TTL, mirror lock-up the R7 is my choice.
Rich
You rarely see a Leica rangefinder used with a motor winder, as it's somewhat antithetical on a small, quiet camera. You also might find the film advance on a Leica is smoother and requires less effort than you're used to. If you want to get to the next frame a little faster, try the trigger-winders mentioned, but I'd agree with SteveS on doing without initially.
