Perry, I've experienced the RD lateral movement issue on my first touring bike. I used the OEM STX 7S RD for the 8S conversion and the RD just makes the shift without any extra effort to the low cog with the low limiter screw backed out completely. It has been fine for about three years now. I've used other 7S RDs on 8+S rears and still required the low limit screw. I haven't yet run into a FD issue.

For BB spindle length I sometimes use an old BB to determine the appropriate spindle length for a particular crank set. Often I've found data on the internet, but it can take multiple search phrasing.

Brad