You can't do too much to a duty gun. It has to be almost stock. You can change the grips, and have some action work done, but not much else. I think a post front sight is a big help.
I use an old Border Patrol Jordan holster. Most guys just use their PPC rev. holster. Anything that keeps it from falling on the ground, and lets you get it out without a lot of effort will do fine. You can find used police duty Rev. holsters on ebay for $5-10.
The ammo has to be 158 grain semi-wads. Talk to 10 shooters, and you'll get 10 different ammo choices. My suggestion is a trial and error approach. Find what is affordable, see if you can hit anything with it, and go from there. If you are an ammo reloader, I have no suggestions. I haven't used my reloading press in 20 years. Anyone want it? Lee progressive.
The 686 is a good gun, I'm sure you'll do well with it.