To recap, We've a Rogue (Swashbuckler)3/Fighter (Battlemaster, archery style) 7 with the Sharpshooter feat. Stats are 8/20/12/10/14/14. Proficient/Expertised in acrobatics, athletics, perception, performance (exp), persuasion (exp), stealth, survival.
General concept: rain hellfire from above/595' away; use some combination of fancy footwork, cunning action, and/or parry to get out of melee if it ever occurs.