My first quilt was made from fabrics left over from the dresses I made in high school. There was everything from cotton to double knit, to chinz, etc. All played well together.

The only suggestion I have:

If this is an item that is meant to be washed at some time - make sure that everything will tolerate washing.

Do some light studying on quilt history and you will find that mixing fabrics has been accepted for years and years. Some of the most beautiful quilts were from the late 1800's and early 1900's -- all of those crazy quilts that incorporated silks, satins and velvets, along with the lacy embroidery stitches used to hold the blocks together. Many of them did not last "forever," but they were certainly beautiful to look at.

I use mixed fabrics all the time. I have used flannels, denims, linens, corduroys, fleece, minky, poly/cotton blends and woolens all with quilting cotton. While I do not prewash most of my quilting cottons, I do however prewash some of the above fabrics before using them in a quilt. You can always make a mixed material mini quilt or quilt block & wash to test your fabrics cohesion and reactions. I am finding that making mini quilts or test quilt block sandwiches is a great way to work through design or quilting issues.

I love to mix fabrics! From Cotton to corduroy, Satin to polyesters, Silk to rayon I love it all. I tend to pre-wash and add interfacing to lighter weight fabics.

I've made several raggy quilts using woven cotton for the top and backing and flannel for the inside layer (rather than batting). No problems but would recommend preshrinking the fabrics. Also made a quilt using both flannel and woven fabrics in the top. Worked fine.

Long ago I made quilts with leftover fabrics I had from making my Girls' dresses etc. The polycotton fabrics looked better than the cottons years latter.
Experimenting is how many things are discovered. There are no rules on making quilts or lots of other things.