6 You can use multiple drives and even network drives to store roms in LB (we are going to drop the P because its the same regardless if you have premium or not)
5 Non-merged or Split (I personally don't understand the emphasis given to the non-merged as the split has always worked fine for me and is half the disc size) For things like Sega Genesis/Megadrive and NES you can use the software list roms in MAME but to use them in LB is a pain due to the naming that MAME uses for them not being supported in LB scraping. Most users just get regular roms and not many bother to emulate console systems through MAME unless it is the only viable option.
4 RA is a great program which offers more than just controller features and shaders it also emulates a few quite a few consoles that aren't supported in MAME yet.
3 By parent MAME I'm going to assume you mean the stand alone version I'm kind of unclear on what you are trying to ask here
2 I don't use bezels so I'm not your guy for this one.
1 I've always just turned the pass to 0 and it worked don't know what would cause it to keep running it at 0