In general your route is good. You don't mention your previous experience driving up/down mountains, so you should be aware of Red Mountain Pass on 550 between Ouray & Silverton. Its steep, twisting, deep drop offs, and no guard rail. Many folks are scared by it and choose to leave 550 at Ridgway on 62 to 145 to Cortez & then 160. That bypass would work good if you start at 4 corners and then make your way east.
Personally, I take my motorhome & toad up & down Red Mtn Pass at least twice a year with no issue, but I've been driving the Colorado Mtns for 30 yrs.
Coming east on 160 you'll also go up & down Wolf Creek Pass between Pagosa Springs and my home in South Fork. Its much tamer than Red Mtn Pass, but still a long steep climb & descent.
Mid Sept is usually prime season for our fall leaf colors.
PS: Since you're driving right near it, you should include the Black Canyon of the Gunnison NP, a seldom visited but very impressive canyon.