Congratulations! October is a good month as is September (when I got married). I prefer fall weddings to the usual summer ones because I won't sweat in my formalwear!

As for rent vs. buy? I would probably go with renting. It's not likely that everyone would be willing to buy an outfit. That's been my experience anyway. I searched long and hard and actually found a shop that rented kilts in one of my family tartans (Graham of Montrose) so I lucked out.

Just take you time and do the research. Best of luck!