I've loaded a bunch of 9x18 Mak... first cartridge I reloaded.
1) I tried cutting down 9x19 brass. Not (IMO) worth the trouble. Several thousandths small in diameter, so had to flare the heck out of it, as well as trim off a mm. And, if memory serves, the bottom of the case was ever so slightly different; can't remember for sure, but think it took a different shell holder? Anyways, I gave up on that project quick enough. Bought S&B (my FEG liked it pretty well), and reloaded the brass
2) the standard .380ACP loads *seem* to be a close starting point - but I would look up WELL ESTABLISHED recipes for 9x18 from WELL KNOWN, REPUTABLE sources (such as powder manufacturer websites, and reloading manuals.
I'm not very brave when it comes to using explosive propellents in a mechanism that I'll be operating right near my face...
3) I ran a set of inexpensive Lee dies for Mak - since the cartridges a few thousands different diameter then everything else, I didn't bother trying to make something else work
For what it's worth, I found that my particular gun would work pretty well with a Berry's bullet over as little as 3.2 gr. of Bullseye. Or, that's what I think I remember - as they say, "your mileage may vary; ask your doctor if this reloading advice is right for you; void where prohibited..."
Seriously, do your homework before trying that load, I haven't messed with those for a number of years, and am out of town where I can't check my records