Dungeons and Dragons

Glad I could help a bit.

From the remix just grab what you like and leave what you don't need. Same for the main adventure. Or any module you will ever DM. It's your game and your player's game, so you decide what happens and what it's about.

As for the potential allied factions I did look at what my PCs were likely to flock to. Then I had those factions contact them. They ended up allied with the gauntlet and Savra Belebranta is a major recurring NPC. They Grey Hand and Force Grey with Meloon and the Blackstaff is another factions the players love. One of the shadier PCs is allied with Davil Starsong and the Zhents. But the others didn't make sense for my party like the Emerald Enclave for example. So I left them out.

The Casselanters have the most interesting story. But it gets dark quickly and the moral dilemma might not be for every group.

The Xanathar is super iconic and a great straight up villian. We will end up fighting him soon now in Dungeon of the Mad Mage.

Jarlaxle is absolutely amazing and likely the most fun villian. Him being fun depends on using his cover identities in fun ways and good roleplay and planning from the GM. He is also vastly overpowered. So there is little chance in the PCs taking him head on.

I found Manshoon not very fleshed out or interesting. So Idk.

You can also switch villians later. If after chapter 2 for instance the player for some reason really have grown to hate the Xanathar even though you planned on using someone else, you can simply change the villian as nothing is set in stone at that time. Also the seasons don't really matter too much. Don't worry about those too much.

Good luck running the game!