Please help me make an artificer artillerist with an extra feat

We're starting a new campaign. I have a very specific character I want to play. Variant human artillerist. (If you're interested In playing him as essentially a retired Army officer from Her Majesty's Royal Arcane Artillery who has somehow forgotten all he knows about magical artillery and engineering and keeps remembering it as he levels up).

My DM has decreed that everyone gets an extra feat at level 1 which gives me TWO feats at level 1 to play with.

You guys are build geniuses. Please ell me how you would build Major Boom for maximum fun and effectiveness. Are there synergies I can take advantage of that change with the extra feat available? How else would you build this kind of character? In my first build attempt I've tried Spell Sniper (wizard) and elemental adept (Fire).

Which invocations would you take at first level? Sixth?

Additional context: The campaign will go to level 10-12 at most. Rest of the party is an Arcane trickster, a bard (lore or eloquence), a Rune Knight, and a shadow sorcerer.