I have the Innovis 4000D and I've used Metro Polyester and Madeira Rayon with no problems. I prefer Madeira Rayon though as the upper tension is not as tight as the Metro Polyester. A tighter upper tension will result in the bobbin thread showing at the top of the design. I've purchased designs from a number of digitizers. Oregonpatchwork is a good place to start. Secretsof is also good. Both have many digitizers listed on their site. If you are into 'Windows' type of design then you may want to try bfc-creations. They are having a Buy One Get One sale on their holidays designs currently.
To do Free Standing Lace, I use Vilene but the designs will come out smaller. If you used Badgemaster or Ultra Solvy (these are plastic like), you get the designs stitched out in the correct sizes.
I also use cutaways when embroidering on knitwears. Most of the time I use tearaway stabilisers. I purchased my stabilizers from Allstitch and American Embroidery Supplies. Check them out. Their prices are rather competitive.
Enjoy your machine
gml