It is definitely a game that doesn't tell you much on it's own. Luckily the community is usually very good about helping new players. You pretty much need to ask to figure out some things. Almost all of the online resources are badly out of date.

And yes the DLCs are ridiculously expensive! In most cases there is an equal, or even slightly better craftable ship of the same class but the permits and quality materials to build non-DLC 1st - 3rd rates are quite rare and usually expensive. It is also difficult to find a good shipbuilder unless your clan has one but DLC ships can just be "redeemed" once every 24hrs. So it isn't completely "pay to win" but not far from it.

The Rotterdam is one of the exceptions. It is like a fighting Indiaman. If you just want to beat up on traders and smaller ships in the Safe Zone and have plenty of room for loot, then it is unrivaled. I don't see may taking it out to PVP though.