There is a point where we can do nothing but go forward and see what happens! I would use the color catchers and wash the project after completion and I would not really worry about the shrinkage. Sometimes I find them at the dollar store and feel they are just fine, usually I just grab a bigger box of Carbona "Color Grabber" sheets when I see one and am getting low at home.
Some color cast is to be expected, it's why jeans fade. If you are really worried, take a white coffee cup filled with boiling water and dunk a corner of the red in there, just a couple of inches. If the water does not immediately look like something you can dye eggs in, you are probably ok. If it is maybe a bit pink after 5 minutes, you are definitely good to go in my book. Any where in-between that should mean a prewash.
When I bought the bag of hand dyed (but not set) fabrics I used in the Bonnie Hunter Frolic project I became an even bigger fan of plain blue Dawn (just a few drops) with rinsing and then a heat seat in the microwave. Using a safe glass bowl, submerge the already wet fabric into plain water, cover nicely with plastic wrap, and heat at high for 7-15 minutes (depending on size of bowl). That's all it should take on a commercial fabric. Those hand dyes took a bit more...
I'm a prewasher by nature and habit and have really only had one time where the dye ruined the project and ruin it, it did! Part of the reason I prewash is because I am sensitive to the various treatments of the fabric and don't starch either, that's actually the biggest reason. The dye cast is two, and shrinkage for a modern produced piece of fabric like a panel is well down on the list of concerns. Depending on the feel of the panel, raveling might be...