There is no right or wrong on these things since it is often a personal preference regarding user interface and features. Personally, I like the RM Lighthouse interface. I find it easy to use. I also like the Hybrid Touch; I often use both the uni-stick button and the touch screen at the same time to quickly go where I need to go. I also love the interface with the iPad.
The manuals reside on both my iPad and on the RM MFD itself. You can view the manual and a chart or radar on a split screen at the same time. Good way to learn the details, but often it is not needed. I found that one good read through was good enough for me for most features and functions.
Integration with legacy ST60s and my 10 year old AP was easy. Used the converter Maine Sail mentioned. Got it for less than $100. Also integrated the new stuff with my old analog transducers (wind, speed, temp, depth) with no problem, using the RM iTC-5.
Personally, I like my setup. (Of course, everyone typically likes what they already have ... can't admit to a mistake, can we?). But this may be a personal thing. I know folks who love their Garmins, Farunos, etc. Go with what you have and enjoy.