You can spin roving into yarn. You can also knit directly from the roving. That's what stuff like White Buffalo Unspun is. Just have to be a little more careful with the yarn so you don't rip the yarn apart since it's a little more... fragile.
With silk, it depends on the quality of the silk, and HOW you wash it. Generally silk is washable, though I wouldn't recommend machine washing the clothes.
Basically treat it like a handknit wool piece of clothing.
Use a very mild soap, not normal laundry soap, but preferably either a detergent formulated especially for silk, or an uncoloured shampoo. Soak the garment in cold/lukewarm water with a little bit of shampoo added to it for 15-20 minutes, gently swirling the clothes around every now and then. Empty out the sink/tub, fill it with water with a tablespoon of white vinegar added, and rinse the shampoo out of the items. (Silk really dislikes alkaline environments, that's why the vinegar is added). Finally, rinse again in cold water, roll up the pieces in a towel to dry (don't wring them out!), and lay flat to dry, reshaping and straightening the seams as neccessary.
Iron while slightly damp on a warm setting, and that's about it.
Oh, and for spot stains, don't just use water. This odd water ring will form, which not even dry cleaning will get out for the most part.
2 inches is quite a big difference for a hat. Particularly if it's a close fitting cloche hat. Since it's a lace pattern, did you check your gauge with it slightly stretched, as it would be when all the YOs are opened up a bit?
As painful as it sounds, personally I'd rip it out and try again with either smaller needles (if your hands can take it), or if the pattern is easy to modify, take out a (or some) of the lace repeats to make the size work.
For marbling, since you're having to dip the paper into the water, as long as the paper isn't that big, you could go taping it to a clipboard or some plastic/metal/non absorbant surface.
As was said before, normally for paints, paper is taped down, sometimes it's soaked in water before being taped down so that it won't buckle while painting. But this is often done with gummed tape (the brown kind that has to be wet first), since it is least damaging to the paper. However, that glue is water soluble, so it might not work as well in this case. Just use masking tape, but remember that if you're not careful and don't wait for the paper to be competely dry before removing the tape, you could tear the edges very easily.
When knitting on circulars (without magic loop or two circs) generally it works best to be knitting something slightly larger than the circ itself. Ideally you'd have enough stitches on the needle so that the fabric is not stretching and straining to fit around the cable, and enough so that it's easy to smoothly slide stitches onto the tips. If you have too few stitches, when you try to slide the stitches around, it pulls on the rest of them and makes it kind of awkward to knit.
The only upper limit to how big you can knit something on a pair of circs is the number of stitches you're willing to cram onto the thing without fears of stitches slipping off the needles.
So if you're using at 16" circ, that's best for things that measure about 17-22 around.
Though as an added comment, 29" sounds rather short to do magic loop with. I've mostly heard of 40" and
I think you're confused about the purpose of blocking.
If you're spraying stuff onto things to make them stand or be stiffer, you should be looking into STARCHING.
Blocking is done to knits so that they gain some "memory" and conform to a shape you want them to. It also helps even out stitches, and for lace, opens up the YOs and empty space that's there for a lacey look.