Welcome Ron

I used to live in Naples...guarded at Vanderbilt Beach while growing up, and used to ply the gulf and brackish backwaters in that area from the canal in our backyard. Great life for a kid

I have an 1987 21WA with a yammi 200 2 stroke and yammi 9.9 4 stroke. RE fuel volume, pop the deckplate over the sending unit and look around for a tank sticker that should state the mfr and the capacity. Mine was a thin aluminum-looking sticker to the left of the sending unit, buried under decades of grime.
Your capacity should be 69 gallons or thereabouts. As you get used to your rig and want to optimize fuel efficiency, I suggest one of these: http://www.floscan.com/html/blue/seriesdetail.php?sid=11
Gives you GPH and totalizes if you leave power to the meter.

Outboard consumption at WOT with a properly trimmed vessel and calm seas can be approximated at 1gph per 10hp. So a 150 should burn about 15gph WOT. These are rough numbers donchyaknow.