Scizor is neutral to SR, but it's still a fine choice, as it resists Starmie's weaknesses and Starmie can cover its Fire weakness. Gengar is still fine as your spinblocker. Flygon isn't meant to defend; it's meant to scout and revenge kill.
Not needed. It's too bulky. Focus Sash is better on very frail 'mons or suicide leads (Metagross is too bulky to be a suicide lead). Lum Berry cures any status Metagross takes while Occa Berry weakens supereffective Fire moves Metagross would take (only once); they're the preferred items on lead Metagross.