Four is about where the game expects you to land, so five is a good run. Our balance test plays a scripted voyage to the end and it lights four beacons too. That's still enough for the top ending, The Lit Coast.
All nine isn't really reachable in two years, and that's on purpose. Each beacon costs more goodwill than the last: 10, then 16, 22, 28, 34. The ending counts islands standing and beacons lit together, so it never asks for a full set.
If you want to try for six: a lit island keeps itself for the rest of the voyage. An early beacon on an island you keep going back to frees those trips for somewhere else. Late on, goodwill usually does more as a beacon than as the last piece of gear.
Thanks for playing it more than once.