Do I need new bolts to install this to my manifold?

The two-bolt flange matches standard manifold holes, but confirm bolt size and condition before install. Reuse existing bolts if they're clean and tight, or grab new hardware from your local supplier to be safe.

Can I weld this flex pipe to my downpipe instead of bolting it?

Welding defeats the flex section's purpose — the whole point is to absorb vibration and prevent cracks. Stick with bolted connection to keep the flex pipe doing its job and protect your welds downstream.

Does this need paint or ceramic coating before install?

Raw steel will oxidize and discolor over time. Paint or ceramic coat it before bolting in if appearance matters to you. Once installed, recoating gets difficult without pulling the whole section apart.