I generally upgrade the hull, aftcastle, and forecastle and discover sectors after 1 or 2 voyages. I keep the rigging lower as it only seems to really influence how long the voyage takes and I'd rather have the other stats. Never had a sector take more than 2 tries so far, might take longer with 15+ (rank 48 so far) though, we try to keep all parts updated as much as possible though. As soon as we unlock a new prototype we make all but the rigging so it's ready to be used once we reach the right rank (and use older (1 or 2 prototypes behind) rigging because of points).