You are correct on the Ring of Color Spray - it is a fixed HP that determines its effectiveness, not an intelligence based saving throw. I don’t know why I had that in my head the other way.
Eventually, I would really like my character to be a classic Fighter/Mage type. I always ended up there in BG1/2, either dual class or multi class. Not having played 5e tabletop, will a multi class fighter mage (after multiclass is implemented in BG3) be what I am looking for, or have the rules changed too much from 2e to 5e to get the same feel without missing out on too much optimization?
If you are just looking for the "mechanical" feel of a fighter/mage dual or multiclass then blade pact warlock might be what you are looking for. Blade pact can get double attack at level 5 just like a fighter, but it is also a full caster (sort of, warlocks are a bit odd in 5e).
Alternatively, when bard is added they also get a full spell progression, and one of the subclasses gets double attack at lvl 5 (or 6, I forget) too. (Note that bards get the same spell progression as wizards and clerics in 5e, its not the half progression that they had in earlier versions... level 17 bards can cast lvl 9 spells, the advantage that mage gets over bard in that regard is a much larger selection of spells to choose from).
Either of those options would let you do both melee and magic without a multiclass.
