I have both the Sherline Lathe and Milling machine, and I assure you they are very good quality machines. (In fact, they can even be upgraded to CNC with parts that are readily available from Sherline, and using your home computer.) I've had both since the early 90's. We bought the lathe first, as you will likely use it more often, for many things. We later added the milling machine to "compliment" the lathe. It is correct that you can turn rims on the lathe, but if you want spokes, or slots in them, you will need a mill. With a rotary table and index attachment on the milling machine, it would be possible to completely make rims on the mill. This kind of thing is the reason I got the Sherline machines..........attachments/tooling are very easy to find, and many times specialized for miniature machining, which is what I do for models.
Granted, these machines are smaller capacity.....but if your main intended use is for modelling, that may not be a bad thing. I would highly recommend the Sherline machines, but as posted by others here, your real expense will likely end up being in additional tooling after the fact, regardless of which you buy. Good luck, and looking forward to seeing the results!