Do I need new gaskets or clamps to install this?

You'll want new gaskets for the connection point between the axleback and factory resonator. Clamps and hangers are part of the assembly. Grab gaskets separately if yours are worn.

Will this bolt straight up to my stock system?

Yes — it uses factory mounting points on the E46 chassis. No welding, drilling, or modifications needed. Unbolt the old muffler, bolt on the new one.

Does stainless steel need any protective coating after install?

No prep or coating required. Raw stainless is ready to bolt on and will develop a natural patina over time. Some owners polish the tips occasionally to keep them shiny, but that's cosmetic.