Fedex One Rate

Hello I recently download ShipRush for FedEx and I a little confused about a couple of things. I ship everything via FedEx One Rate (Express Saver) and ShipRush only gives me the option for a FedEx pak and nothing else. Do I select FedEx Pak for everything? Also I have to put in a package weight but for One Rate you don't have to specify a weight, should I just 1lb for everything? Lastly when I estimate that rate of the package it's more than double what the price for One Rate should be, am I missing something?

Thanks in advance for your help.