For both locations, you'll definitely need reservations 6 months up. I've already booked dates at Moraine Park, and did so early on the day that the window opened for that date. And even doing this, I still was not able to get my first choice...or 2nd choice. September and October are still very popular for Moraine Park, as Glacier Basin usually closes right after Labor Day, so it's the only one open in that area, and the elk will be rutting...generates a LOT of traffic there.
6 nights in Rocky? For some, too many. For others, not enough. Depends on what you want to do, besides going up on Trail Ridge Rd.
There has been an uptick in the number of bike riders up there, and while some of us are tolerant, most tourists are not. There's been some dangerous incidents with bike riders, both going up and coming down. Going up, the riders are going very slow, and as pointed out, there's no bike lane, so you're in traffic. Tourists don't like that. They crowd the bike riders and I've seen some passed very close to the rider. Going down, the bike riders are going very fast...sometimes way too fast to stop safely if needed, and there are a lot of blind curves. And don't forget you'll be at elevation up on Trail Ridge, between 10000 and 12000 feet. Oxygen depletion is rapid. My suggestion -- don't even try to bike ride on the main roads in Rocky. Bikes are not permitted on most of the trails in Rocky. There are plenty of other things to do in Estes, and there are bike trails all over town and in the valley.
And there's LOTS of hiking, on both sides of the park. Shorter hikes are mainly on the east side. Longer and sometimes more scenic hikes are on the west side. Of note on the west side are the Grand Ditch and the hike to Lulu City, following the headwaters of the Colorado River. Each of these could be a day hike, depending on how adventurous and experienced you are.
Also on the west side, Grand Lake is a must see/do. It's a good day trip over there, good places to eat in town, and most of the activities around the lake are still going on in September. Plus there's some really good hikes that are short and scenic near the downtown area.
