Your DWR is very nice, love how you used the prints on the rings and the solids on the corners. The next pattern you have picked out will look good in the prints you have chosen. As a LA quilter, my advise would be just to make sure there are no snaps on the jeans items, and mark any really thick seam areas. Use some blue tape or pin pieces of paper over those areas. Cannot wait to see your next quilt. Your friend is going to be blown away by your wonderful choice of quilts.

I longarm, and Dunster is right. Shouldn't be a problem. I have done a bunch of quilts out of clothes for people. I've used my robot and freehand both. I just pay attention and slow down. Just be mindful of pressing correctly and trimming loose threads. Also, let your longarmer know if you used stabilizer just as a heads up. My machine will sew anything when I take my time, but not all machines are the same.
What you are doing looks great.

Of course you can use multiple textures of fabric in the quilt - just respect the nature of the fabric and you will be ok

However, before you make one and expect it to be longarmed (if someone else is doing the quilting) talk to that person first and get advice. He/she may not want to quilt a multi textured quilt.

Wow.... your DWR quilt is one of the prettiest I have ever seen and what a GREAT use of the ties!! Love your inspiration quilt for the other fabrics too.... what a nice thing for you to do for your friend! I can't wait to see the finished works of art!