It isn't so much how many stitches there are for cross stitch. If the stitches are entirely covering the design area you will need different stabilising than if the design is in a more traditional style. I have stitches some of my own designs in a traditional style without stabiliser at all. Instead I have used linen and starched it before stitching. The one in the pictures, I used matching bobbin thread so it looks good from both sides.
Anything over 10,000 stitches, Floriani recommends 2 layers of tearaway or I layer of cutaway. (Don't hold me to this - I'm working from my memory of their instructions.)
I use linen and one layer of tear-away stabiliser - for this biscornu as well - and it works fine for me..