Since Wishes is scheduled more than an hour prior to your ADR time, I'd nab a good spot to watch from the train station inside of MK. This puts you conveniently close to the exits.
Promptly exit the park after Wishes, and either hop onto the Resort monorail or take the boat launch to the Poly. The boat launch is located to your right, just in front of the monorail station. This should provide you with both an excellent fireworks viewing experience, and get you to your ADR in plenty of time.
IF you do not have park admission for the day, then I'd seriously consider hopping a ferry boat from the TTC c. 6 PM. They say the view of the fireworks from the ferry to MK is wonderful! Almost like having a Wishes cruise.
Or, you can always watch the fireworks from the Poly grounds... then shop or just wander the garden paths afterwards, until your ADR time. The marina/boat launch is a really good spot for viewing. The area near the volcano pool is also very popular (you could even grab a pre-dinner drink at the pool bar, if you like).
Lots of options.