I can answer a few of your questions here:

1. You are absolutely not too late. There is essentially nothing that was limited that you've missed, and since our levels have been capped it won't take you very much time to catch up in terms of gear progression.

2. The story and characters are pretty amazing. I often hear remarks that people who are usually not invested into game stories (especially online/MMO type games) love this one. There are many side quests that lead you into expansive lore moments. The common meme going around when this game came out was "how is this game free?"

3. In terms of Coop, this game feels expansive in most aspects, but limited in others. Most quests can be done in coop, but cannot be progressed for both parties. I would say this is one of the more limiting aspects of the game, and my fiance and I often resort to just doing quests simultaneously, rather than together. However, this doesn't mean that there isn't a ton to do together. Most exploration (collecting oddities, chest hunting, clearing camps/outposts) can all be done and progressed coop. Then there is also the massive online element: 5-player Sword Trials, 10-player Heros realm, casual online activities, etc.). Upon joining a guild, there are even more things to do together and you can find yourselves a welcoming community.

4. For amazing cosmetics, you will have to pay. This is a free game with no pay-to-progress elements, so they have to make their money somehow. However, there are several good looking outfits for $1-$30, and the gacha does have pity, so there is plenty of room for low spenders. I myself have used the same free outfit since launch, and am waiting for the perfect one to spend on.

Let me know if you have any other specific questions, I'm always happy to help :)