I have the 300E and love it. When I first got the machine, like yours it just set for quite some time. Albeit, I don't use the machine everyday but super happy that I have it. I do have Embird and create most all of my own designs. Whenever I need a gift for someone, I embroider something special just for them.
As far as stabilizers, I buy most all of mine from Walmart. I mostly buy lightweight fusible Pellon and a mid weight tear away. So far this has worked out just fine for me.
Regarding threads, I mostly use the C&C embroidery threads but if I don't want a shine on the embroidery, I use Maxi-Lock serger thread. I do use the Maxi-Lock serger thread as my bobbin thread.
If you want to embroidery on something with loft, towels or fleece, I do suggest using a water soluable on top to keep the stitches from sinking into the item. DO NOT buy a lot of it. Humidity can make it a globby mess.
If you want to embroidery on knits I do suggest a "sticky back" stabilizer. You only hoop the stabilizer, and you stick your project on top of the hoop.
If I can be further help to you, please let me know. I'm more than happy to help fellow sewists.