This is a good question you pose. I think the balance between those three factors (crowds, hotel availability, and # of attractions) is pretty decent at the moment. My family goes almost every year, and we usually end up going either between may and june, or between july and august. I'm wondering if June and July has peak crowds because I have never found the crowds at the time that we go to be unbearable. Although I have noticed that Toy Story Midway Mania always seems to have a super long queue with a wait time of 2 hours or more. I haven't been on it in nearly 3 years.
I think the number of attractions is great, but Dsis and I usually only stay for a little over a week, so we never get enough time to REALLY see everything Disney has to offer. For me, Disney has enough to keep me busy and entertained for three weeks straight, but there are those that complain of the lack of variety and new things to do. I have noticed Disney doing refurbishments and repairs more often in the last few years, and maybe it means it's time for Disney to think about revamping some rides completely and adding on some new linchpin attractions--HOWEVER there are some classic rides that I believe should remain at the parks forever as they are part of the Disney magic and nostalgia (e.g. Carousel of Progress). If all of the suggested new projects that are floating around the rumor mill come to fruition, it could be very good for Disney in my opinion, and help to keep a better balance of those three factors.
We usually stay at moderate resorts, and never have trouble booking rooms.