I see you live in Texas -
you might want to venture over to the RRC forum and see if anyone is doing a build and needs a hand to get your feet wet help someone else, and figure out how to use the tools...
my 'shop' that has gotten me by consists of:
Air Die Grinder with carbide bit
Chop Saw
Sawzall
DeWalt 18V drill
Air compressor to run the die grinder
DeWalt 4.5" angle grinder (cut off discs, grinding discs, and sanding discs)
I borrow a torch when I need to cut a lot of material or make plug weld holes...
I borrow a JD2 (JDSquared) bender when I need to bend tube.
I have a Lincoln Weldpack 3200 HD 110 Mig welder that has done 'okay' on the projects ive used it on.
I think I do 'ok' as a home fabricator - but ive spent a LOT of time with the wrong tool figureing out how to make the right ____________ (cut, bend, weld, hole, shape, contour... etc)...
the hard part is figuring out what the end goal you want is, and how to get there with the tools you have...
As for materials -
for round tube that I need to bend, the bender I borrow only has 2 die sets - 1.25" OD tube with a center line radius of 3.5" and 1.5" OD tube with a CLR of 5.5"
Ive been able to get by with this combonation for a while.
For roll cages, 1.5" OD tube, .120 DOM is good for external, structrual members, 1.75 gets used from time to time on some rigs, but I think the tube OD looks too big for our cars... 1.25" tube is much too small for outside members, but can be good for bumpers, internal members and whatnot...
HREW dents pretty easy, DOM is harder to dent.
.188 wal tube is harder to dent than .120 wal tube...
Tube is generally called out by the OD and the wall thickness...
best of luck!