What a great project. Wish I was still building I would take this on in a heart beat. Mr. Eranomo, What you are asking for is more than we as a hobby do. But, some of your needs are doable. I see your two biggest issues will be 30mph and 4 hrs of run time. I would suggest looking into electric motorcycle forums for engine and battery options. You can always us an adapter on the shaft for a prop. I would love to see a 8' Aluminum jon boat tethered to a pole in the middle of the pond. at the pole attach a remotely operated winch in which you can let out line/rope in order to land and change batteries. To the line you can attach streamers etc. On the boat behind the prop install an air driven noise maker.
Not knowing what your ponds look like you may want to seek a cheaper alternative route! Tethered electric float planes with screaming noise makers and streamers.