easywdw.com lists those days as "5" and "6" on the crowd sizes, so busy but not terrible. Friday, it's Epcot that's the "red" park, and Saturday, it's Magic Kingdom and Hollywood Studios that are the "red park. So I would say time your park visits for early morning, and avoid the "red" park for the day and you'll be fine.
The reports of FP+ lines coming out of the rides and blocking sidewalks were on days with crowd estimates of 7-8-9. There is a big difference between "5" parks and "9" parks, believe me! On a "9" day, it's hard to get through anywhere in the park on a
scooter. On a "5" day, you need to watch where you're going & take it easy, but you can get around fairly easily.
We have been there several times since FP+ started (including 11 days already this year on three different visits) The worst crowd day we hit was a "5"...the FP+ lines did NOT come out the rides at all. There was one occasion when a FP+ line backed-up, but that was because the ride had been down (Big Thunder) so they were allowing people who had fastpasses during the down-time into the line too. That slight mess cleared after about 30 minutes, though. Every other FP+ line was completely inside .
I am on a scooter all day at the parks...the only time it is difficult to get around in those medium-sized crowds is parades during the day, and right when they get over (people are dispersing every which way) Also at the park entrance at arrival time (we arrive before rope drop) and then again when we exit if we stay for the last night-time show/parade/fireworks.
Have found it better to try and be at the front of the pack at rope drop, and wait about 20-30 minutes before we try to leave the park...crowds thin out quickly and it's easier to go.