Congrats on the sewing machine, Kendall.
So the seams for the tyvek backpack are a combination of thread and tape. The thread was polyester, I think I got the regular size from Gutermann at Joann Fabric, they also had a heavy duty. The pieces of tyvek that I had were on the smaller side so I often had to join 2 together to make a larger piece, and that was done with adhesive transfer tape like the stuff mentioned in earlier posts. I found it to be amazingly strong. I thought of making the whole pack with only taped seems, but I had a hard time picturing how it would all come together and have the shape that I wanted. I would still need thread to attach the mesh pockets and straps. Sewing tyvek is definitely different than most fabrics, and is really more like paper. Dupont recommends about 5 threads per inch and it works out pretty well, giving a fairly strong seam without tearing apart from the perforations. Never the less, I still went back and taped all my seams. Primarily it was to add strength, but also to waterproof it. The hardest part about sewing the tyvek for me was ending the seam. Usually you can back tack at the beginning and end of a line, but that doesn't really work, so I just relied on the tape to keep the thread from coming undone. I'll have to come up with a project where I can play around more with only taped seams. Perhaps a tyvek tent will be next...
Oh, and watch out for sewing through that tape - it will gunk up your needle and make a mess. I found I could use a little bit of wax on the needle if I had to get through a spot that I had already used it.