Rachelle - Hm. Well for the postcards (and all my cyanotypes which are traditional formula and I'd say they are pretty close to cyanotypeII blues, sorry David and Dr. Ware ) I use a straw like a pipette. It can take a little practice to get a feel for how much sensitiser a paper can take. The BFK Rives I used in the exchange is almost like blotting paper so it sucks up quite a bit and the aim is to get just enough liquid on the paper that you can make smooth brush strokes but not so much that it puddles.
The "antique-y look" definitely sounds like a paper thing to me. There's some cheap cartridge/inkjet paper I have used that has that issue.
When you're starting out, it's good to just buy small packs/single sheets to start out with, just to test. And sometimes the paper company will just change a product so you have to move on and find a new one. Cyanotype is prima donna