lvl-5 bottle is usually 1 grid away from where you found a bottle and easily "zerg" by just a regualr (even lvl-1) bear tame. It gives you around 250-300 gold. So it's actually matter of couple days - sailing sloop and digging a treasures. Also check shipwreck. Lvl-10 is around 300 gold. Lvl-18 around 600-700!!! I once got 2 wrecks next to eachother - one lvl-16 another lvl-18. Lucky me!!!)
Then you go Schooner, and things go global. Go to NE island at C6 to catch a high lvl Tiger (caution this island has insane wild animals spawn so building not just a trap but also a shelter - highly recommended). And do all high lvl maps (don't forget to wear an armor and drink grog before fight. Tiger also drinks a grog btw, but his buff goes for only 5 minutes). It's tricky, do to lvl-20 map with tiger but his bleed attack goes long way.
The only thing you should know - if damned warrior (or solder) don't swing his weapon for a while - he buried underground and restore health. So you have to make him swing and avoid attack. To do so - you either move backward or hit him before he hits you. Patience, caution and let the bleed do all work (it's around 5-10% of health per hit).
So you go global. Do treasure. Put couple of ballistas to stern and do whales quests. Do mermaid quest. And do alot of discoveries. I personally go to a grid for the first time (if there is no goldens there), dig treasure, and do all landfalls this grid.
So count this phase of a game as "earning gold and max levels". By the time you'll get your 18k for brig you'll probably have max-lvl around 60+ (enough for all in captaining skill tree), and then you will be able to join the battles on BRIG.
There is just a one problem. Game still instable. There is a risk to hit whale or damned legion camping a grid border. And... well... you can loose your Schooner right the first voyage after you get a ship. It... happened to me. Game just crashed and didn't allow me to log in until my schooner was destroyed. Can you imagine how unhappy I was that day!!!
As for trading... it's... wel...
I mean it's super stupid and boring. You put 3 prefab building, set your trading routes, and wait until you'll get some resources you even didn't set for trading, and also gold around 1500 each day. You just don't understand - why you get all those resources. You see like 90 pages of logs per day with messages like: "You shipment 923759832475983749 was sent" "You shipment 1123412341231212413987931234124 was complete". I mean... It made really weird way. It's like "money for nothing" and you don't get how it's actually work.
After a next wipe I WONT even try to set those things up again. It's better to explore the world and get gold. I don't know why devs don't wanna us to do that...