Cast on Knitting stitches for an afghan/gauge

[laurebelle26]

Hello, I am starting my first afghan and am very excited as I have just gotten my yarn and all my circular needles. My question is two fold

one, what is the best cast on method for afghans? and where can I find examples if I am unfamiliar with a specific type?

Two, The pattern calls for me to start with a smaller needle and then change to a larger needle. Do I need to make a test gauge for both needles? ( I really don't want to but I never have good results if I skip it.)
Thanks so much for any input.