If I buy a phone without memory or minimal memory, can I change to a memory card that I buy somewhere else? I was thinking of a class 10 32gb or 64gb.
Are there any concerns with doing it this way?
Are you talking about removable storage (microSDXC)? It's not required, and it's expandable up to 64GB.
Without removable storage, you will be using the built-in storage which can be either 16GB or 32GB.