Here's my 2 cents.
Medieval + Hints of Renaissance
Astrophysics - Don't care. So long as it's practical.
Navigation by Starcharts/Magic Power Sources - Practical, possible, and ok by me.
Atmosphere - Eh... personally I'd prefer to stick with "Earthly" and blame magic for any flying of objects that shouldn't otherwise fly.
World Building - I prefer option 2.
A pangaea world could be fun to an extent. I would prefer a pangaea in addition to a few small outlying landmasses.
If I were to claim a piece of it, I think it would be really interesting to work with a Pangaea style landmass that had been split from a smaller piece of itself at some point by an angular impact crater which subsequently filled with water. I'll claim the southeast part of the Pangaea for that. Something like a peninsula that had been struck and separated by the primary landmass by an asteroid... maybe creating a large island and a few smaller ones and forking the land at the impact site. Perhaps this part of the world is also on its own tectonic plate, and it's got some mountain ranges on the western and northern borders, and a series of mountainous folds in the northeast that cause a locking in of moisture and wet weather patterns for that area, making the north shore swampy and giving the mountainous terrain plenty of rainfall, but the south shore doesn't benefit from this and stays fairly dry, with the west shore a comfortable middle ground. Domesday book demographics suggest six major cities. I'll say 4 coastal, 2 inland.
Something like this... would be an interesting place to develop.
Map Divisions - Squares are easy to work with, and practical. If needs be, someone could take more than one square to get the territory they want.