cowanw is bang on concerning the Exposure Preview Lever. You have a superb kit - the 50 1.4 Planar and RTSII was a classic combination in the early 1980s and the RTSII, unlike the original RTS, has a mechanical fail-safe of 1/60 if your batteries fail. The Yashica FR1 is a lovely, solidly-made camera which uses the same Sugaya shutter as the RTS - its only flaw is a tendency for the film counter to fail and a fallible self-timer, though both can usually be fixed. Your Yashica lenses will serve you very well - especially the two ML (Multi-Layer Coating) types; the DSB is an earlier type that has only a single coating. Some of the Yashica ML lenses outperform their more expensive and illustrious Zeiss cousins, specifically the 21mm, 24mm (sharper and more contrast than the Zeiss 25mm), 35mm, 55 2.8 Macro, 100 3.5 Macro (a stunner!), 500 f8 mirror (better than the Zeiss Mirotar and thought to be the best 500 f8 ever built!), plus the 28-50, 70-210 f4 (very rare) and 100-300 zooms. The standard lenses - ML 50 1.7 and 1.4 are great performers too. The RTSII is a lovely camera to use and with Zeiss glass still being very expensive, those in the know are buying the top Yashica ML lenses instead - but their prices are already moving north.
Have fun with your Contax/Yashica gear. I have dozens of their cameras, lenses, data-backs, bulk-backs, winders and motor drives, Polaroid backs, flash units, etc etc and my original 1977 RTS is still going strong...so you could be enjoying that Contax feeling for many years to come!