You are essentially asking "tell me how the universe works, in 25 words or less" so expect a long-ish
learning curve.
The SeaRay could be on OK choice for you, but... it'd be better if you start with a list of features yoU NEED, features you'd LIKE TO HAVE, and features you DON'T WANT.... and another list of activities you expect to do on a
boat (long trips? short hops? hang out in your marina? etc.)... then go find boats that match your lists. If the SeaRay still shows up, it'd also be good if you could than also compare that to other similar boats... see which really bubbles to the top.
Once you've got a viable short list of boats, it helps to go aboard and imagine yourself doing chores and other expected activities, If you intend to cook, imagine
cooking a typical meal. If you intend to do your own
maintenance, imagine changing
oil, filters, impellers, zinc anodes... and imagine winterizing if you're in a cold area. Imagine showering, or
washing dishes. And so forth...
Fuel is not usually the highest cost factor; more likely dockage, maybe
insurance after that, fuel or maintenance next (latter especially if you hire all your fix-it/service-it
work, at $100/hour for example). Then fuel depends on how far you travel, and how you do it. If you run a
diesel SeaRay 400 on plane, figure .75 NMPG... so trip distance dictates. If you run at
trawler speeds, figure as high as maybe 2 NMPG in that SeaRay if it's diesel... and trip time dictates.
Note also there's a choice to be made between gas and diesel; valid arguments for each, but the short version is usually that gas is good for short distances or
dock queens, diesel better for longer distances. This is a "pay over time" (gas) versus "pay upfront" (diesel) comparison. Note also there are some additional safety-related activities you need to do with gas, not onerous but also really important.
It is normal to make a powerboat
purchase subject to a
marine survey (hull and so forth) and a mechanical
survey (engines)... to try to eliminate
buying someone else's problem... but you should know these are also not infallible.
Typical production powerboats like SeaRay and similar are these days usually fitted out with
electric appliances, including water heaters.
Propane is less common, except for some of the trawlers and heavy long range cruisers, and diesel heaters/cookers even less common -- with exceptions, especially for custom-built (or modified) northern boats. Then again, boats like that SeaRay are designed with the idea of marina-hopping being most likely, and many
shower ashore. And boat people often do "Navy showers" -- get something wet, turn the water off, soap up, water on to rinse... repeat..
Still, unless your showering habits call for 30-minute showers, you will never run out of hot water with an 11-gallon
heater; the re-heat rate is very good. (We have an 11-gallon water
heater, two showers sequentially, never have run out of hot water.)
There's some reading you could do and some courses you could take. Chapman's Piloting is a good start. The USCG Aux
Boating Safety Course, and the US
Power Squadron equivalent, are both very good, you'll likely find important.
More folks on trawlerforum.com (sister site) who can speak better to powerboats, so you might stick your nose in over there, too...
-Chris