Great advice from TF members!
Lots of good comments posted for our new member. I especially commend Firehoser75's comment on 10% of the cost of the boat being spent annually.
Chartering - best idea, but you can probably find a day charter, whether fishing or otherwise, to test sea sickness.
Repairing. Smaller, sound boat might be a better choice than a bigger "project boat". Give that some thought. If you're inland, smaller makes good sense. My 31' was fine taking New Jersey off shore on well researched good weather days - RI to NC delivery voyage - but ocean travel is not in my future plans. Wilmington NC to Philadelphia is my target range. If I had a larger boat, I might amend that. But, I can accomplish a wide range of destinations and cruising experiences with what I feel are reasonable limitations, precautions and objectives.
Find a friend with a sailboat on big water, even a big lake. A windy day under sail, healing enough to put the lee rail under, take some green water over the bow - you'll know about sea sickness quickly. I'll bet you can find some folks who were sea sick initially, but "got back on the horse" enough times to overcome it with or without medication. You'll probably find some on TF. Many trawler owners are former sailors. (Cooking below decks on an alcohol stove in lumpy seas, under sail - I found out the limits of my motion tolerance. Had to come up for air every 10 minutes or so.)
Fuel is the least expensive aspect of owning a trawler. Insurance, slip fees, boat yard repairs/bottom paint, and discretionary purchases - marine stores and catalogues can be enticing - a test of character!....., then there's updated electronics, and more..... It does add up to 10% of original cost on average, and I'm guessing more for an older boat that's not in top condition. (I tell my non-boat friends that owning a boat makes owning a horse look smart. Owning a boat costs much more.)
Single engine. Read Steve Zimmerman's article on engine life and % of effort - diesels need to be run hard enough at intervals to clear out the exhaust system. A single engine running a little harder, say 20% to 35% of WOT GPH might be a better choice than two running at lower RPM. Plus, maintaining two engines does cost more. Letting a second engine "feather" is a false economy - doesn't save much fuel, and risks overheating your stuffing box on the free spinning prop. Look at Nordhavn as an example of single engine dependability - ocean crossings on private single diesel trawlers.
Main thing is that you're asking the right conditions in one of the best places - TF. Consider taking a Power Squadron boating course or two, and ask the instructors about their experiences on the waters where you live and plan on boating. USPS is outstanding for instruction from supportive, helpful, experienced boat operators. Join USPS and attend frequent meetings, dinners, seminars, etc....one of my best choices.
Best wishes for your boat dreams coming true, especially if you keep asking good questions of boaters experienced on the waters you intend to cruise. By the way, most of us started exactly where you are - dreamers who did our homework, listened, and put dreams/resources/goals/feedback into a formula to come up with a workable and realistic outcome. (Watch "Captain Ron" to see the alternative way to get into cruising.)
NCheaven