A big question is
whether I should use a conventional gasoline/oil based motor or go with
electric.

Easy to calculate running times for any given trolling motor and battery
combination. Now calculate or observe your hull speed. Now you know your
best possible range. Derate that for possible problems.

My bet is a battery does not store enough energy to do what you want. The
energy density of a lead storage battery vs gasoline is ludicrous.

Think of that 50-pound trolling battery as a gas tank that holds (the
equivalent energy of) a pint of fuel, takes all day to "fill" (recharge),
costs $$$, and wears out in a few years.