Forums ate my post. Twice. So here goes, in shorter version...
[1] That's fair and probably for the best. We do want to offer a fair bit of variance, after all. I'm wishing now, even more than usual, that I possessed even the slightest tinge of artistic talent so I could try to relate some idea of what ranges of weapon designs I think could be varied yet congruent, and interesting without being impractical.
[2] I think I need to ask more about the weapon before I can fairly start, because that involves one of my core complaints, but there's also very little detail on it so far.
I've been imagining it as being capable of both (far-reaching) spray and use of projectile. I imagine the weapon itself would look something like a flamethrower in that it has a barrel from which fluid payload can be launched or added to another, and may be optionally ignited, electrified, or saturated with further aether, etc.. But I figure it would best also would hold, in cohesive fashion, a few other normally modular parts. Among these would be a way to (1) dispense the normal payload in burst via projectile, at range, perhaps through the use of a material cask produced inside the weapon itself or through some manner of "Shell" spell, meant in either case only to last until impact or near impact, or (2) launch an alternate payload summoned materially from some depository as with MCH devices.
The first -- if allowing the projectile 'bay', so to speak, to bank resources -- would make the projectiles' use would integral to typical gameplay as a sort of balancing/filtering system; after all, you'd effectively be filling it via the normal flow or by diverting some part or characteristic of the normal flow. This means it'd be tied whatever's normally going on, though perhaps as a foil to your purposes for your spray. For instance, you could purify your canister even when no useful target is present, or just continuously over time on toggle command, by flushing toxins into the projectile chamber, causing a particularly potent-to-enemies projectile while increasing the potency of your spray to allies (and perhaps decreasing its simultaneous damage to enemies, though you can always change how favorable the extremes should be for that, if at all). Such could be like a maintenance mechanic done right, in that it wouldn't just be maintaining a single optimal outcome, but always allowing preparation towards some strategic payoff.
The second would allow you more direct manipulation, similar to ammo types. You summon X, put in the gun, and can either launch it immediately at its full payload, or you can choose to filter it into your normal stuff for additional potency or X effect.
Or you could take both. Or whatever else; those are just spitball ideas.
The point is, though, that you have a highly technological job with at least a pretense of great ingenuity and complexity; the weapon that allows for all that must, if fully fleshed out, therefore hold a trove of mechanical possibilities to work from. I'd like to see that from the toolkit. The weapon is your base for everything. Start there. Rely not one bit on skill templates until you've maxed out the options inherent to your weapon and its likely accessories (e.g. a hip-attached chemical injector/ejector or whatever else).