Transitioning from LMOP to POTA

I’m wondering what kinds of options i’ll have for transitioning from lost mines if phandelver to princes of the apocalypse. Will I need a subscription to move characters for my players? Is it possible to just buy both and open both games in one campaign to get a single larger campaign?

PotA is a module, which means that it only can be added to a new game. Your can enable the Character Vault in both games, which I think is on by default. You or your players should be able to move the characters using that. At the subscription levels, Plus adds Dynamic Lighting, and Pro adds the API and the Transmogrofier, a way to move almost any object from one game to another.