Storing items inside the crafting windows for extra carrying space?

Yes, you can even abuse it to stack stuff that is normally not stack-able like wands in the crafting screen and then pull the stack out. If you then use the wand and it burns out, it'll look as if the entire stack is burned out, but if you unstack them again inside a crafting screen only the top one will be.

I haven't had any problems doing this with saving yet, but then I play with permadeath so I rarely save.

Some might consider this to be an exploit, but since this is a single player game it is up to you to decide if want to use this trick or not.

Yes, you can - as of patch 1.0.2. So the Smelting, Smithing, Alchemy and Tinkering each grant 4 spaces, while the Still gives you two. The Elven Ingot Grinder yields no benefit, except that you've got a Grinder of course!

I've noticed that there seems to be some strange things going on with respect to saving, the Grinder and the Lutefisk Cube but I can't put my finger on it just yet; I always lutefy grinders, but I sometimes find them with things I've lutefied/grinded in both the input and output positions. Probably a small bug swapping two object positions in the save file. I'll put up a screenshot if I ever come across it again.