1) I'm not sure the orientation the white one was printed in, but I printed the green one right-side up with full support material, then removed the supports by hand (you can't really tell in the pictures, and can barely tell in real life--the FlashForge Creator Pro is extraordinary at creating easily removed ABS support).
2) The person who printed the white one told me they did the finish with clear coat. The only snagging that would have happened seemed to be in the area where the yarn comes out--the rest of the inside of the bowl is quite smooth. If you look closely at the close-up of the yarn coming out the front, you'll see where I filed those edges down. After filing, the yarn comes out quite nicely.
3) The green bowl is 100% infill, but you're right, it's still pretty lightweight. I don't have experience using it (girlfriend knits and crochets, I just look on in awe), but my uninformed opinion would be that it may work if you put something smooth and heavy in the bottom. I notice she only uses it when she's laying on the couch knitting, and it's usually nestled down in some of the blankets to keep it in place.