Well glad you got going relatively economically.
Now, as you said, you're on a fixed income, so IMO you can't afford to "keep" a 6.0 diesel.
Even half the ford nut swingers will tell you to dump it. If it runs you'll do ok selling it. Not great, but blow a hg and spend another 5k bulletproof ing or lose more than 5k selling a broken truck.
And yes, coolant filter needed/that issue. Ficm etc.
or keep it. It'll be like going to the casino every time you drive it. Sometimes you get lucky!
6.0s are now an economical way to get a kick butt diesel truck IF you don't mind spending some bucks and are handy with a wrench. If your mechanic skills are limited to swiping a credit card at the repair shop, do your best to get away from the 6.o.