Installing three motion detector outside lights at daughter's house. Power to come from panel in basemen. Wiring on outside of building will be surface, either pvc or emt conduit. No aesthetic issues due to location.

Question: How do I change from romex inside the garage to conduit outside the building. Rumor has it that I am not allowed to run romex in conduit (overheating??). If I do the change-over in an electrical box, it has to be accessible. Not doable in the to-be finished basement with tenant. I suppose an outside weather resistant box will be required.
Any ideas?
Also, is there any need for a switch? Three lights, three outdoor switches? Circuit would be from a dedicated breaker.
Lights are so the tenant can walk down a long narrow sideyard, turn the corner and go down the stairs to his unit.
All help appreciated.

Ivan Vegvayr