I just wanted to add a note to this thread, as I'm currently running Baldur's Gate: Descent into Avernus. For anyone who wants to have your PCs pursue Tiamat to hell and finish her off once and for all, be aware that she features rather prominently in Descent into Avernus. If you are thinking of...
I actually find that this makes quite a large difference in character concept.
What does being born to power mean in a particular family? A particular society? Do you hide it or are you open about it?
What led you to make the trade for power? What sort of being did you trade with, and how did...
It depends on the campaign and the players. For players who are new to the game, I like starting at level 1 because it introduces the features gradually. For those who are more experienced, especially if it's going to be a short campaign, I am more likely to start higher.
I actually think Dragon of Icespire Peak (aka the Essentials Kit) is that expansion. It adds a ton of side adventures to the basic Phandelver setting and brings the party level up a little.
Is this your first M.T. Black adventure? I recommend "House of the Midnight Violet" for another project. It's one of my personal favorite adventures. (Also "The Clockwork Queen," which was co-written by Black.)
When my players killed the white dragon in Dragon of Icespire Peak, I used this supplement to determine what they could get and what to do with it:
https://www.drivethrurpg.com/en/product/276213/hamund-s-harvesting-handbook-a-complete-guide-to-harvesting-and-crafting-in-d-d-5e
The group has already played Lost Mine of Phandelver (I forgot to mention that in my original post). I think they'd like a longer campaign ideally, though.
I think it's fine if you get player buy-in. Just like playing earlier editions, some people would love the thrill of deadliness and others would respond by becoming paranoid in an un-fun way about potential character loss. Neither approach is wrong. Just find out which one applies to your group...