The IIIS can use the same 45mm f/2.8 xenar as the IIs, as well as 28, 30, 35, 50, 85 and 135mm lenses. (although the DKL mount 45mm f/2.8 xenar was designed for the Instamatic reflex and does not couple to the rangefinder in the IIIS. In my experience, the 50mm f/2.8 Xenar is a superior performer, but that is based on my sample size of one each). The 35mm f/2.8 Curtagon is also a lovely 5 element design lens.
The IIS does not have parallax adjusting framelines, it has projected framelines, but just with parallax correcting marks visible in the frame. The IIS is reputably more difficult to service than the IIIs, because while it has a simpler RF/VF system, it's compressed into the smaller retinette sized body.
Both the IIS, IIIS and Retina Reflex S, III and IV models use an EV lock system without any EV numbers essentially. The two knurled knobs around the lens mount adjust the shutter speed, but couple the aperture to it to keep consistent exposure. So when the shutter speed gets faster the aperture gets wider and vice versa. The wheel on the bottom adjusts only the aperture unless you hit the end range, in which case it will then bump the shutter speed one click.
So basically, if you want to use it by ignoring the meter you can, you just need to set the shutter speed first using the winged knobs and then set the aperture with the wheel. There's no way to disable this system without significantly modifying the camera.