Mid to late July and August. Hot enough to make swimming a pleasure. Usually pretty good weather. As for bugs..... In 10+ years of running the Main Salmon, the only bugs I've seen are yellow jackets, and they are always around. I've never seen a mosquito on the MS. I don't carry bug spray.
My favorite outfitter is Canyons Inc. based in McCall. I know many of their guides, and both their current & former owners quite well. Top notch outfit. Most of their guides have been with them for many years and they are excellent "river stewards" not just college kids with a fun summer job. Great knowledge & love of the river, awesome food, awesome service. They usually run oar rigs, paddle rafts, and IKs on each trip,so you can take your pick. Let them know up front if you want to IK the whole time. Shoot me a PM if you want more info.