Would it be possible to have us need only one portal? For example: We build the portal and add a Biome card and a major card. When we open that portal it shows two lists, one for Biome cards and one for major cards. All the possible biome and major destinations would be shown in the two lists. If we have not yet added a card to our portal, it would be greyed out and unavailable for porting. Once we add a card to that portal, the option for that realm would become available for us to select for porting. In this manner, we would need to build only one portal and could use our build limits to better advantage.
You can still use only one portal and make it back to realms you previously visited you just waste cards and have to keep making them. So long as you dont choose the option to reset the realm then you can get back to them when you add the same cards. I only use one portal at the moment. I like the suggestion though, its a cleaner design and would be helpful to see a list to choose from.