Can we add interfaces permanently? so that we won't need to add it again when we open the GNS next time.
You can't, but you don't need to either.
There's a little trick you can do. Here's how I described it in the GNS3 Network Simulation Guide
You can get GNS3 to automatically add appropriate modules to your routers by holding the <Shift> key when you select the Add a link tool and select the type of link you wish to use. When you now click on a router, it will automatically add a module of the correct type and connect to the first port of that module
Disclaimer: I am the author of the GNS3 Network Simulation Guide
-a VMware image of Ubuntu with GNS3 and VPCS installed and a collection of exercises/labs