One of the best trip we ever had (in 27 yrs of 2/3 trips a yr) was the time we went Thursday to Tuesday the weekend before Halloween weekend (it fell on a Friday that year). The weekend closest to Halloween tends to be very busy, but the one before was wonderful. We attended
MNSSHP - it was not overly crowded, but festive. Crowds were great - not the least we'd experienced, enough to keep it festive, but no real lines - Soarin' was new then and we did not even need a FP for that. It was an excellent time to go.
If possible, you might want to consider switching to Wed 21st or Thursday, 21st to Wed 27th or Thursday 28th to avoid the days closest to Halloween weekend.
It is a very nice time to visit - although last yr was hot, it was perfect during our stay - cool mornings and low to mid 70's midday.
Have a wonderful trip!