The standard method on Kickstarter is to double the pledge amount (you can also do this after you pledged) if you want two of the same reward type. If you want to combine different rewards, the math is more complex... but hey, you are smart... you can handle :)
When the campaign is over, we will send out surveys to make sure we know exactly what you want for your pledge money.
Remember to add the shipping costs. And yes, the monthly fee is tied to the PM so you will pay one fee per PM.
Hope this helps - and sorry this is a bit cumbersome (the idea is to remind you that Kickstarter is not a regular store :).