Sig SB15 arm brace & buffer tube for it from KAK Industries.
Vortex SPARC II optic.
I thought about doing a left side charger when I built my 300 BLK SBR. You will get gassed badly if you ever decide to put a suppressor on it. I decided against it for that reason & the non-standard parts configuration.
I would shoot it first before dropping much $ on a muzzle device. We shot my friend's 8" without a muzzle device & the blast wasn't that bad, 300 BLK is efficient with the shorter length barrels.