#1 How much gas are these babies going to suck back with “normal”
cruising?

1mpg is typical for boats of that size/style. That's 26 gallons per
hour at 26 mph. Anywhere between 19 and 30 gph is to be expected.

#3 Is 1200 hours a big deal on a supposed well maintained engine?

1200 on gas engines is not a small amount. Around 120 hours is a
typical amount per year for recreational use. So you're looking at a
boat that was being used for less than the typical amount. Or that it
sat for some very long stretches without the engines running. This is a
warning sign. Boats (or anything else) that goes unused usually means
they've also been neglected. Or there was something 'really expensive'
to fix and they postponed it well past the economical repair stage.

Please help A.S.A.P. as I am taking it for a test drive Monday or
Tuesday.

Pay for a survey. Do no buy a used boat without one. Yes, this will
cost you a couple hundred. Spend it now or prepared to get reamed for
several thousand in surprises later.