The first project I ever attempted for my car were aluminum intercooler tubes.

Couple of things I found that may save you some headaches:

I was pretty happy with my first sets of welds. I decided to grind them off to clean up the look.....HUGE MISTAKE.....this lead to countless pinhole leaks along the weld. I wound up laying another bead over all of the welds I ground off. I'm certain a more experienced welder would have had cleaner less pourous welds but that was not my case at all.

Butt welds on thin wall tubing are difficult. Somebody suggested getting scraps and practicing, definately follow that advice. I wound up with 4 stacks of 2" long rings of tubing all welded together about 2' long each from practice welds and I was still barely able to produce consistant welds on the real pieces. This type of weld on thin material is hard to do....I also did some similar welds on 4" aluminum tubing with a wall thickness about 1/8" and those were easy....the thin stuff was rough.

You will need some kind of jig to hold stuff so you have decent angles to weld. Straight pipe is easy but your stuff will have all sorts of twists and bends so holding it at an angle that makes your life simple is not often easy to do.

In the end my rookie welds aren't going to win any beauty contests but I pressure tested them at 40psi (2x working pressure) and there were no leaks. The simple pleasure of learning to do something like that myself was work the headaches.

Good Luck