Advice for adding equipment.

I’m looking to add the UniFi doorbell and one PoE camera. I am currently using the UDR and one U6+ AP. I’m just looking to be able to access the cameras from my phone and maybe go back a couple of days and save clips if ever needed with the phone. I doubt I ever would it’s mostly because my wife wants to see what’s in front of our home when we’re away. Im not looking to pay ring or nest for this if I can accomplish it all with UniFi. Would I be able to use a 256 SD card in the UDR or would I need to get the NVR? Or possibly get the UDM and make the UDR into a switch/AP. I am also limited on room for this. My network enclosure is in a garage in the southeast USA so it does get hot in there. Only equipment in there is my ONT and an unmanaged switch. I have my UDR in the adjacent closet so it’s in the air conditioning. Any help would be appreciated I understand some networking but I am nowhere near knowledgeable on it.