We've moved up from a 20 Grady, then the 25 Sailfish and have now enjoyed our 2001 Marlin for the past 8 summers, 15 Bahamas trips and nearly 900 hours on her. We had "dreams" of a bigger boat, etc but as I get a bit older, I realize that the Marlin fits really well within my/our needs. On two Bahamas trips, we've spent 18 straight nights aboard, showers, cooking and everything!
Think of your fuel tank selectors as a fist with a forefinger out, "pointing" to the tank that's being used. Locally, I run one engine off each tank so that when I add fresh gas, both tanks get some. Feel free to swap the selectors around to keep them flexible and moveable. Same with all your sea cocks....... open/close/open/close.... just exercise them to keep them from locking up on you.
If you only use your boat on occasion, I would suggest that you do not top off the tanks. I'd rather add 50-100 gallons of fresh gas more often than to run the risk of many months passing while you wait to burn down the 306 gallons of gas that the Marlin holds. No doubt, there are other opinions out there about this, but this has worked well for me over 3 Gradys and 15 years of regular boating. Get educated on the use of Ring Free as well as any fuel stabilizers......
If you have a genset, "try to wear it out" by using it! My trusted Genset mechanic says that he replaces 95 out of 100 gens from lack of use, versus from them being worn out! Crank it up, let it warm up for 5 minutes, then "load" it up with the Batt Charger, Water Heater (make sure the tank is full), run the AC, etc. When it's time to shut it down, "unload" it, let it idle for another 5 minutes to cool down a bit and then shut her down. Don't forget to get that fully serviced when you do the engines. Even at the dock, when I run the engines, the genset gets run and exercised.
Have fun and post a few photos!!