Welcome to the site to the both of you!
Plenty of info ready for your absorbance here! I would suggest browsing around other peoples projects and getting ideas of the kind of things you could make so that you get an understanding of how things go together and how they work.
Not very many people here start off with a set of plans. Most of us just go by what we want the end result to be like. You're gonna have problems once in a while, but don't let that stop you from trying something else.
Things to take into consideration, along with what Ironman said are:
What kind of material: Steel tubing, angle iron, square tubing...?
Engine: Motorcycle, single cylinder honda, clone, briggs, etc,
Drivetrain: Torque converter (recommended for off road use), clutch, etc..
I'm sure there's more to think about, but I can't think much at the moment, (just got back from my programming class, LOL).
Have fun and good luck!
