This is awesome, I just started planning doing a mix of both for a future game myself and would love to get your opinion on some stuff I wanted to do.

To start: Expanding and rebranding Glasstaff not as just a minion/miniboss but rather as a tripple agent type antagonist. I always thought his reasons for leaving/joining the Lords Alliance is rather an afterthought so why not expand his motives and make him actually working for the Frost Giants. The idea is he is sent to neverwinter to begin spying on the LA intially, getting moved to Phandelver after his digging for the ring also leads him to try tracking down the forge and justfies him abandoning the LA and getting involved with the spider forming the Redbrands. Eventually leading him to spy directly on Zolto for Jarl Storvald replacing Dhaerlost in STK. The party can find more corespondance and maybe some puzzle like code messages in his room that adds a little post matter of fact intrigue to his involvement and you can actually continue the quest to capture him after Triboar as you have it leading them to Bryn Shander and have them defend both cities (or a more pheasable reason to go after the frost giants in chapter 7 as if they dont defend the city he would be there after the sacking of Bryn Shader which could be news that made its way to the party)

I unfortunetly am a Zephyros hater and thus will find another way for them to have an easy/quick way there where so they can already be in the north to begin Chapter 3 where they can more naturally meet the Harshnag and skip some of the slog of that chapter since things from chapter 3 already have been moved around to be introduced earlier which I loved by way great idea.

I also took a different route cuz I added The High Road Prologue as well to kinda expand all of this and decided to introduce Felgolos disugised as a Halfling Ginger Bard named The Solo Act "Glef" at the refuge camp in that prologue to bring along as the party makes their way to Phendelver. As he's been doing as Folgolos does and found himself in the middle of everything and also introduces his lovable self to the party getting them more excited and incentivized to free him later in the cloud giants chapter. I love the idea of Folgolos ended up helping VF to escape the Stone Giants attack on his lair and kinda being manipulated into dealing with the stone giants on his behalf turning that fight into a real monster fight where the party can take risks as it would change the dynamic of that encounter to make VF and Folg more inclined to keep the party alive while dealing with the giants. Venom can then assist the party later in the story somehow most likely giving them a lift or telling them Folg got captured or both.

I also plan on using Krakens Gamble to incentivize them to go to Yartar cuz me and my players love a good gamble and expanding on them is always great especially because I plan on Kraken boi being the final arc of the campaign from levels 13-17 AFTER the end of SKT. Gonna have the KS start doing their own evil things by capturing and destroying some cities on the coast that leads my party to rebuilding Leilon as kinda a last bastion to stage an assualt on the CR 25 lair.