Growing up on a farm, my father never believed in doing anything more than changing engine e oil every three years. So in the morning I'd head out with, say, a tractor and plows. Normally before noon I'd get to walk back to the house because something had broken. So my father would call over my Uncle to fix it. Uncle worked at G.E. welding turbines, so after a long day there he'd have to drive 30 minutes to come and fix the 'widget' that broke.
Being g a young kid I would get frustrated with this system and would stay with my Uncle out in the field. Father had (still has) a wicked temper, so whenever something broke it was somehow my fault. So staying out in a half plowed field was far better than the other option. Got to learn a lot from my Uncle. And soon I was fixing the equipment myself. At 10 years old I rebuilt my first engine. It was by no means perfect, but it lasted 5 or 6 years until Father blew the water pump belt, but kept going as it appeared a steam locomotive was coming down the hill. Somehow that was my fault.?!
That's a long story to say...
Life is so much easier when your equipment works. And your equipment works if you maintain it well. Start by getting new fluids. New belts. Fix all the problems you find. Then you can expect the machine to work for you. And then you can make it better by building it the way you want. You will know the vehicle and what needs improvement and what dosen't. And it will be far cheaper in the long run.