I agree with most of what was said above. I'd caution you against spending lots of money on a set-up for this gun. Once you gain some experience, you may want to go in a different direction. Sights may be the biggest drawback of the model 64. If you chose this platform because it will be what you use as a S/D weapon, then more power to you. But it sounds like you are interested in the "game" aspects. At least any gear you buy for the 64 would be usable with a 19 or 66 should you decide you want better sights.
You can save some money on a speed loader and speed loader holders. Buy an HKS (model 10) to use for the initial cylinder charge. You're not on the clock and they are about half the price of a Comp III. Definitely use Comp III's for your reloads during the COF.
Safariland makes simple (read that cheap) metal speed loader holders. They run about $10 each. For the longest time I was under the impression these were not legal for IDPA. A recent perusal of the current rules revealed that they are, indeed, legal . Perhaps this was changed at the last rules revision, or perhaps I was wrong all along. These slip over your belt. Some people modify them by making a 90 degree bend at the end of the retaining leg that goes over your belt, so as to lessen the possibility of pulling the loader and holder off the belt when all you wanted was the loader.
For a holster, I'd recommend a Blade Tech. You can adjust the cant and they carry the gun correctly (front strap above the belt), they also cover the trigger as required.
Ammo? Round nose is a must, especially if the charge holes of your cylinder aren't chamfered. I use PMC Bronze 132 gr FMJ RN. Federal AE also makes a 130 gr round. Some prefer the heavier bullets (158 gr).
My gun (a Brazil 586) has some work including a Wolff RP mainspring and 14# rebound spring and some smoothing of contact surfaces. It runs about 98%. Every now & then I get a light strike - certainly not desirable, but I have put more effort into my other competition revolvers, and they run 100%.
I'd dissuade you from USPSA with the 64. The revolver division is owned by the 8 shot 627's, 327's and 929's. Plus you will need a lot more gear in terms of loaders and carriers. IMO, the only credible gun that could be used for both is the 625 or its variations. A speed loader driven, minor PF, six-shot, 4", fixed-sight revolver doesn't stand a chance - unless your name is Jerry or Masaad.
Shoot some IDPA, with a minimum investment until you figure out what may work better.
Here are my competition revolvers...
Good luck and have fun.
Adios,
Pizza Bob