How does someone approach the Trails series? It feels like a Kingdom Hearts scenario. If that's the case, I am staying away.
Depends of what you mean by Kingdom Hearts scenario, but it's fairly straightforward. There aren't any spin offs that aren't really spin offs here.
They're a series of games with an overarching story and continuity, that are divided by narrative arcs, with each arc taking place in a different country of the continent of Zemuria, with a different cast of characters, and a somewhat self contained plot. I say somewhat because it has an overarching story, which means that things builds from what came before, and not all mysteries are resolved by the end of an arc. However, as they follow a new main cast, the different arcs can be enjoyed without previous experience with the other games, although they obviously enhance the experience.
The games are as follow (with a newly announced game still in development):
The Liberl arc
Trails in the Sky
Trails in the Sky Second Chapter
Trails in the Sky the 3rd
The Crossbell arc (not available officialy in english)
Zero no Kiseki (Trails from Zero)
Ao no Kiseki (Trails to Azure)
* There's rough fan translations available for both, although the one for Ao/Azure is in a far better state. There's also a proper fan translation project for the first game (Zero) that has already finished and they're in the middle of testing and ironing out bugs (they will also add features that have become standard for the series in the west like Turbo mode). Should release this year, relatively soon.
The Erebonia arc
Trails of Cold Steel
Trails of Cold Steel II
Trails of Cold Steel III
Trails of Cold Steel IV (still not realeased in english)
As long as you start at the beginning of an arc, you will have a good time and will be able to follow things and get invested. If you're worried about missing things like deeper lore knowledge, references, knowing certain characters beforehand or getting spoiled, then obviously start from the very beginning and move up. The first 2 Cold Steel games and the Crossbell games take place simultaneously and there's overlap in terms of plot events, so they can be moved around in order without much trouble.
If you have more specific questions I can try to answer them.