MAME and MESS and multiple console systems

[Sandman71]

I could not find this answer, so I apologize if this has already been discussed.  Somewhat of a noob, but have been learning A LOT. 

I have Maximus 2.10 running with MAME 183 and a few other non-MAME systems.  Thinking of adding a few more consoles that say use MAME (or MESS- which I know merged).  It took me so long to work out the MAME/Maximus config, I'm afraid I'll muck something up. 

My question is:  For the additional consoles which can also use MAME/MESS- like Atari 7800, C64, Intellivision, etc.  Do I need to run the MAME install program and have a completely separate folder for each of the files and exe for each emu?  I actually downloaded MESS .151 and was thinking of just using that instead of even playing with fire installing MAME.  Or do I just "point" to the different ROM folders in Maximus while using the same (and only) executable? 

Thank you in advance!

S-

(Windows 10, 64 bit)