Here is an idea for the settlements that players will encounter and where they can trade and rest, and their populations.
- 100 miles: Golden City (50,000), Red City (30,000), Purple City (40,000) Main Sea Ports
- 50 miles: Orange Harbor (5,000) Cargo transfer site for ships going to either the Golden or Red City.
0 miles: Blue City (10,000) Last city before the wilderness, launching harbor for expeditions.
10 miles (1 day): First Outpost (5,120)
30 miles (2 days): Second Outpost (2,560)
60 miles (3 days): Third Outpost (1,280)
100 miles (5 days): Fourth Outpost (640)
150 miles (8 days): Fifth Outpost (320)
210 miles (11 days): Sixth Outpost (160)
280 miles (14 days): Seventh Outpost (80)
360 miles (18 days): Eighth Outpost (40)
450 miles (23 days): Ninth Outpost (20)
550 miles (28 days): Final Outpost (10)
After that it's only friendly locals at best, which can only offer shelter, food, and some healing for trade.
I might be using an XP for gold system, maybe alongside a system of XP for discovery. In that case, characters get XP only once their treasure has reached the Blue City and goes into a vault. Until then, it still can be stolen or otherwise lost, and the players don't get a reward.
Alternatively they could get the XP as soon as they reach any of the Outposts or a protected fort they establish in the wilderness. I can imagine maintaining larger ships and paying crews could be a great permanent money drain, making the loss of money hurt just by itself.