The Paizo Ultimate Campaign has rules for:
1) Exploration, even for creating the map as it is explored.
2) Buildings, for if you want your characters to settle between adventures.
3) Kingdom rules that blends the above to make nation (it does not have to be a monarchy)

Also about tech trees, you could take a look at Civilization games. For example:

Take a look at optics (related to making caravels, that could traverse oceans) and work from there what should be available (techwise) to your players.

[wow, this forum is strict about posting: no posting links bellow 10 post in total; no more than one post per minute, i had to make an unrelated post somewhere else and wait to meet the criteria]