There's nothing wrong with using Mo. Bullet Co's. 18 Brinell bullets. I use them at even lower velocity in my .45 ACP loads. The trick to eliminate your leading issues is to use a cast lead bullet that is .001" over the barrel's groove diameter, you don't need to go any larger in dia. for proper obturation/bullet seal. So, yes, you need to slug the bore and you can make slugs from old fishing sinkers or you can simply use a soft swaged lead bullet and if you had access to some that were .358" that should be large enough in dia. to cover any potentiality as far as the Ruger having a larger bore dia. From what I understand, if you don't mind waiting just a bit longer for delivery, Mo. Bullet Co. will custom size your bullets to the dia. you need and again, anything over .001" greater than groove dia. gains you nothing but increased pressure at the same powder charge.
You might want to consider a slightly slower burning powder as well, and personally I like to use dense spherical (ball type) powders because they meter better and flash less. Better metering will help ensure better consistency of chargeweights. One powder that's not quite as dense but is still a spherical is WST. It will give very good case fill in 9mm to at least 100% load density once you work up to the mid charge level. Data for 9mm is a little hard to come by, though. A good dense ball powder that can be used in any handgun load would be Ramshot True Blue. Like Unique it's as versatile, but being a dense ball powder it meters better than anything else you're likely to use and there's very good cast bullet load data @ www.ramshot.com
and ZIP wouldn't be a bad choice either for cast lead loads, but True Blue would be better for when you load jacketed bullets as well.