Second (third) the rolling stand or dolly pod for sure. Hand held 4x5 would be tough.
Also, you imply natural lighting, which could produce very long exposures, although Ed Weston lived with it.
I would start with 4x5, try some and see how it works. Even 4x5 could be longer exposures, depending on the light quantity.
The general rule that I was taught for traditional portraiture (above the belt with the head) would be the sum of the two film sides (9 inches for 4x5, so, slightly telephoto).