Sounds like you had a blast!
A long time ago I tried running a Seafaring/ Pirates themed sandbox game. The first two adventures had clear goals, but no set way to accomplish them:
- In the first a famous pirate tests potential crews, in a sort of a find-the-hidden-treasure hunt in a series of small isles, against other groups.
- In the second they got betrayed by the fsmous pirate, but also hunted by an inquisiton fleet force, and they had to escape the series of isles.

The two adventures were spectacular, and the party did things I never expected. Some of our best games! But... as they escaped, I sought to enable them to pursue whatever adventure they wanted, provided various hooks and such, but the campaign faltered and stopped... I later realized that the players wanted some clear (or semi clear) goal, and some way to pursue it, and disliked "just sailing to seek adventure"... You seem to have thought about this, and prepared some direction in advance, to provide enough motive for exploration, while leaving enough freedom to explore and undertake interests on the way.

Reading your log so far, ignited a desire to try something on similar lines to what I tried before. If I may, some questions?
- I am contemplating between 5e, Pathfinder P6/P8, and... Dungeon world. (I've been exposed to it lately). Any thoughts? Especially from the GMs side.
- part of your campaign takes place on ships. Are these just as means of transport, or do naval travel rules and naval combat come into play? If so, can you direct to a good one? I tried using 3.5 Stormwreck before and hated it, and read the PF Skull & Shackles AP naval rules and disliked them. Any recommendations?
- Any particular system youll be using for the wilderness/ hex map exploration?

Thanks, and please keep up the log! I'm enjoying it. :)