Need Advice
 

I was gifted with several 24" squares of linen. Some are 100% linen, some are 50% cotton and linen, and some are 60% Viscose and linen.

I want to make a lined jacket using the squares. I can use the viscose/linen to make a pair of shorts. Would there be a serious problem using 100% linen with cotton/linen? The weight of the fabric is the same, just the content is different.

Viscose is another name for rayon. Linen initally shrinks more than cotton. I would personally preshrink and preshrink again all the squares and then send them to the cleaners, not wash them at home.
Linen usually won't press wrinkle free unless you have it professionally done. I think you will have a beautiful jacket. What will you line it in?

You actaully can get linen to press wrinkle free, the key is to iron it while it is slightly but evenly damp.
They can all play together well if they are pre-shrunk, and are of similiar weight. I personally would not make shorts out of any fabric with a high linen content. The wrinkles, as the garment is worn in this case specifically in the groin area, are not very becoming/flattering.

That's great to know. I figured the cotton and the linen would probably work together, but hadn't thought of pre-shrinking.

I also scored a couple of yards of a tan colored silk. That's going to be the lining.

I got the fabric from a freecycle type group here in California. There are a lot of designers who have fabric scraps and they donate the scraps and everyone takes what they want. We donate a small amount ($15 for a paper grocery bag full of fabric) to help defray expenses and the storage building.