I've made stuff sacks from Tyvek before … the primary issue is tearing, especially in area's where it gets worked a lot. Otherwise I don't see any issues with it.
You make one the same way you'd make any stuff sack …. fold a piece in half, sew along two sides, fold over the top and sew the drawstring channel, turn inside out.
For more advanced stuffsacks, you can square off the bottom.
Here's some more complete instructions: http://thru-hiker.com/projects/silnylon_stuffsacks.php.
You can make a bivy out of Tyvek as well if you're really tight on cash. Just make it like a big stuff sack about 36 inches wide and 76 inches long. sew in some bug netting on the top and put a drawstring along the very top.
For a Tarp ….. I would recommend folding the edges over about three times to make a thick drawstring channel all the way around, then run paracord thru the channel all the way around. Tie loops in the Paracord at the corners (and leave gaps in the drawstring channel where ever you want tieouts). stake to the paracord instead of the tarp material and your tyvek will last a lot longer.
I tossed together a SUL packpack the other day out of some scrap Tyvek I had laying around …. it looks like it will work ok for light loads. Loads above 20 lbs probably won't give you much durability in the material.
One last thing … you can spray paint tyvek. Talk to your local printer shop and they can probably recommend what type of paint to use along with an airbrush. You could make some pretty cool designs if your artistic.