mik

Coaster brakes are ok if you add a front brake to the bike.
A few folks are happy with just the coaster brake only, but coaster brakes can overheat and the grease inside them bakes to a useless goo which leads to complete failure of the hub. They do require maintenance like any other part of the bicycle, a bit more frequently when used on an MB.
I am not familiar with the quality of the Huffy Panama Jack frame, but if it is of suitable quality it could make for a fine MB.
As for the best kit to use, that question has started wars!
All of the kits have their merits and drawbacks.
You need to start out with these question:
How do you plan on riding your MB?
Flat ground or hills or a mix of both?
How much will your rig weigh, yourself included? (Don't share your weight with us, just keep in mind how much the engine will be moving.)
Where do you want the engine to be placed?
Will you be riding in inclement weather?
How much time do you want to spend maintaining your power train?

Do you want to go fast, or just cruise

Welcome to the sight mik! We have a lot of Great Guys here, you should have no trouble Buying, selling , and trading! Not to mention the wealth of knowlege here to tap into! Good luck on your projects!

Welcome to the forum. The Panama Jack should work fine if it has a steel frame. Aluminum frames have developed cracks on occasion.
I agree with GearNut on the coaster brake. Take your time with the build and it will save you hours of troubleshooting later. The experts can pull off a 4 hour build, but most of the rest of us can't without muchos problemos tarde.