First off, the very first thing you buy as an upgrade to your starting ship should be cargo space, this will help you make money quicker to buy your way up to your next ship, which should be priority number 1 once you hit 4000~ Sov's, buy the Pellinore-class Trader Locomotive.

Once you have the Pellinore, you will unlock 2 aux slots, I recommend fitting these with the Pressurized Cannery (provides Butchery + 4 cargo space) and a mining drill, and perhaps a cabins (I recommend sensible plumbing)


This should be your basic standard set of modules and ship for your duration in the reach, it should (provided skill and luck) be adequate for most everything in the reach until you can build up enough money, stories, items, quests to head to albion.

Once you reach Albion, you should have built up quite a considerable stockpile of various goods, possessions and sovereigns to head to London, stock up, prepare and be sure to bring a decent gun (marauder's cannon or better) and set out on a journey to find the Royal Society.

Once you reach the Royal Society, it is here where you will be able to finally min-max your Locomotive's modules. Immediately you should go to the Portsmouth Arsenal and trade in as many things you possibly can to the mechanic as possible- You will need to have AT LEAST 9 things to turn in, but I recommend having 19 or 27 you can find a list of the items that can be given to the mechanic here. -
[ https://sunlessskies.gamepedia.com/The_Royal_Society#The_Portsmouth_Arsenal ]


Buy these items in numbered importance.

1. Carmilla -25 mirrors- This is the most important item to acquire, as it is a cannery, which instead of using your Aux slot (the most important slots) It will use your crew/bridge slot, meaning you will have an extra aux slot while retaining butchery and as an added bonus it also provides +4 cargo space.


2. The Rosetti Cabins -25 hearts- These cabins provide very little crew space (only 2) but also provide 8 armor, as they are equipped in the armor slot of your locomotive, and since you have sacrificed your crew slot for a butchery, these will compliment each other. *note: if you replaced your original crew slot with the butchery, you will lose the crew if you dont have the space to provide for them.*

3. The Prosperina Drill -25 veils- It's the least important on this list because it is just the same exact aux drill the standard drill is, but comes with +4 cargo hold, there's only 2 other drills in the game that are arguably better and only 1 that is 100% better, which is also gained at the same place but further down the quest line and higher mirror cost.


And there you have it folks- 2 aux slots, with 3 aux modules equipped, this will allow you to equip an Assaying device, on top of butchery and drilling meaning you get to have all 3 Aux mods, without using the (1) best ship in the game to have 3 aux slots by default.