You might also want to try http://image.online-convert.com/convert-to-svg , I've had very good luck with that site.
No worries on the bit size, Easel will automatically just not carve any detail too small for the bit to fit into. On something that complex, you will see a very significant loss of detail at an 8" size if you go larger than a 1/16th, I'd think. Your best bet would be to use the two-tool engraving method they have, and use a 1/8 or 1/4 or so to clear the bulk of it, then go to a 1/16th for your details. At least, that's how I would tackle it if I was using Easel.