First off, congrats on the 5 star base (lightning), she's not super strong due to power creep over time, but amazing for a good portion of the story AND arena (which can give a few nice pieces of gear and some nice lapis).
Snow can be a decent tank, garnet can be an alright healer early game. The units listed can get you through a good portion of the story.
While lapis is currently abundant, I'd recommend making some bags bigger, which it does sting a bit, it is permanent and you'll eventually make use of it. I'd personally recommend 100 unit/materials to start, materia/items take a lot longer to fill out and aren't necessary early game.
Hoard as much of the lapis as you can, eventually a really nice banner will come along and you can get the best bang for your lapis. Worst case I feel we'll have a players choice banner in June for our 1 year anniversary.
I wouldn't recommend trying to farm trust master just yet, it's a lot more efficient with higher energy, and if you get to learn about Valentus, he shows that you can beat content without them. That being said, there are certain trusts that are more valuable at the start, and saving the trust moogles for them is a good move. Dual Cast and Dual Wield are top tier.