Generally we just don't know a lot about Instein controllers and support in OnStep release-4.24 (what most use here) is basically an educated guess that seems to work. I have no desire to become an expert on them either...
Now, feel free to ask specific questions about OnStep in general and I'll comment on these specific issues you mentioned. First let me say please read the Wiki, learn how to flash your controller (with the software in my Github account or from Instein's sources if you can figure that out) you'll have to become your own expert, this is DIY here. ;)
For meridian flips be sure the Preferred Pier Side is set to East.
Be sure the Meridian limits (E/W) are set properly and such that there is an overlap region (where the flip is allowed.)
Be sure the controlling software is configured to trigger the flip in that overlap region.
This works for many users of both SGP and NINA.
For the guide rate issues... I will only say there are two guide rates in OnStep. The normal guide rate and the pulse guide rate. The pulse guide rate is remembered across power cycles and is only set/changed when a guide rate at or below 1X is set. You can set 0.5x once then go set higher rates all you like and the pulse guide rate will still be 0.5x. The exact behavior is described in the Wiki. Also, technically the pulse guide rate is an optional feature but usually enabled by default in recent OnSteps. Pulse guiding is used by my ASCOM driver.