I have portholes.
I found in the summer there was no problem. In the back cabin, which I'm using as a studio, there is one porthole (small), a pigeon box and a side hatch.
Through the winter I've experimented with LED lights which are proving good.
An advantage of portholes over large windows, which you might want, it's easier to hang delicate artwork out of direct sunlight. I've some prints and drawings which would spoil in sunlight.
Personally I like portholes for privacy and security.
And, for fun, you get some cool looking reflections on the ceiling and walls, even better with the odd mirror specially placed.
All the best with the artwork.