I like the wishes FP because we can have some room and are able to sit down without having to camp out a spot. And it's a good view for the projection show before wishes
With MSEP, I feel like it's not needed as a FP because you can basically stop anywhere along the route and have good spots to view it. Can get some really good spots in over by splash mountain. But however if you don't mind using a fast pass for it, then go ahead and do it.
As far as following the parade..you could but I wouldn't recommend it because that's what all the other people are going to be doing. It's normally wall to wall people going down main street toward the castle after MSEP.
For wishes FP preference. You can go to either side, but we prefer the East side, closer to Tomorrowland. Get a lot better view of Tinkerbell when she flies from the castle. Also I think it's a lot easier when you're leaving. A lot of people use that walkway where the west side Wishes FP lets out that leads into the shops and out to Main Street to head to the exit. So it's constantly crowded after Wishes. With the East side Wishes FP, after a couple minutes the crowds have died down by that exit and you can head toward the rest of the park or go join the crowd to exit. Also if they have the backstage exit open, it's right there