Soy, that's a great list of companies you've compiled already. Make sure you have some sort of a tracking tool to remember who you signed up with, your usernames/passwords, etc.
Also, track shops that you have applied for and have been assigned. There is a spreadsheet that one of the members posted [
www.mysteryshopforum.com] Even if you don't plan to use a spreadsheet for tracking, take a look at it so that you know what information you should track for every shop. I use that spreadsheet and have a tab with the MSC info, such as a link to their sign-in page, my u/p for that site, the type of shops they offer, when and how they pay, etc.
Sounds like you're off to a great start. Congrats.