The Sierra is one place that you can actually do a trip by flying and then using public transportation. Reno to the Sierra and back is pretty easy. But if you rent a car lots more trailheads open up for possibilities. If you do the Wind Rivers or Sawtooths I would think you have to rent a car. May not be an issue if you all share costs.

Post Labor Day in the Wind Rivers is going to be more uncertain with weather and nights definitely colder (freezing most nights). September is a great time to do the Sierra. Only problem this year is that we have 20% normal snowpack, so it will look quite dry and there is a high potential of forest fires. Many small streams will be dry.

This is just one suggested loop. North Lake - Humphreys Basin - easy off trail side trips all over the basin, French Canyon - Merriam Lake, x-country to Bear Basin (Feather Pass, class 2, moderately difficult pass- have to deal with talus)lots of great off-trail but easy travel within Bear Basin, faint trail back to PCT, up to Marie Lakes with nice side trips to Melody Lakes, up Piute Canyon back to North Lake. This loop can also be done from the west side taking the Ferry across Florence Lake. Could also go from Humphreys Basin to Granite Basin (trail route via Pine Creek Pass or off trail via Royce Lakes),and then take Dancing Bear Pass (more talus)into Bear Basin. Not a good route if uncomfortable with class 2 passes.

Good guidebooks are "Sierra South" and "Sierra North", if you want to see more all-trail routes.