what is the best tool for carving glass?

This is a broad question.  Is carving glass hot or cold?

Carving hot, there is not a best tool.  It is more of what tool works well for the artist.  Some great materials are graphite and even a knife.  The tool needs to be able to withstand a lot of heat

For carving cold there are also many tools, and rather than the best, what is the best tool for the project?  Some use sandblasting and just a graphic.  Some use a diamond bit in a Dremel and some use a diamond saw.

will there ever be a spinner cap for The EOK?

No, with the pedestal in the middle of the dab dish one can only use a very small pearl with cap.  This pedestal also causes air mix issues making it hard to spin.  The next issue is that if one used pearls, they are so small the can get sucked up for a hard inhaller.

We find that just moving the carb around can move the oils all around the dish heating as you want.

has anyone ever made a water pipe out of pyrex?

If you mean pyrex dish wear, yes and no.  The new Pyrex is a unique soft glass that can withstand thermal shock.  The old Pyrex dishware was used by blowers back in the day.

If you mean do they still use Pyrex Boro tubing?   Yes.  Elev8 Premier uses Shott glass, there are many brands of borosilicate glass.