The best way to make money the first time around that I know of is through selling special alloy which costs 350 per unit in the imperial gate then selling it to the hiigara flagship shipyard at 550 per unit. its cargo size is small and the distance needed to travel is also short which is probably cost and time efficient.

After that the next best way is through humanoid computer production which is bought in the Alios region for around 1m RU. You need certain items to produce this item but the cost is definitely less than the earnings you get. The humanoid computer sells for 350k per unit in the imperial gate and uses around 500 RU to produce 1 of em which extremely time and cost efficient in the long run. You can also buy multiple production units to make them faster.

Now are you looking to buy the huge flagships you see being used by the fairy empire like the queen battleship or even the alios fortress. There is a secret jump beacon in imperial mining colony at 320 this jump gate takes you to an unknown sector in this sector there are black market shops that allow you to buy this huge flagships and many more but they cost around 1 billion RU and use 600 pop cap know that this black markets spawn randomly so you need to enter and exit the region again if the black markets dont spawn.

To get the vagyr controlled space you need to find the secret jump locations they are located around the angel moon and outpost of hiigara. you can also press the button "T" and a map of the mod will show up.

Some missions give rewards that allow you to buy ships there is one in the alios region and 1 in the vagyr region

not sure if this is true but after some testing, increasing your popcap also increases the scaling of ships in battles so I recommend to buy the popcap and upgrade or buy new ships immediately.

Know that the trading tips I gave only works for the 1.05 version its completely different for the 1.30 versions of the mod which is not translated. In the 1.30 version it takes a while to progress the game due to the ranking system it adds a bit annoying but there are ways to progress faster in them. as for the secret black markets and missions in 1.30 there are still mostly the same with new ships being sold and new rewards being given to some missions.