Do I need hose clamps for this reducer?

Yes. Use hose clamps rated for silicone on both the 1.25" and 1.50" ends. Standard worm-gear clamps work, but stainless steel or T-bolt clamps grip better and won't slip under vibration.

Can I use this for a boost line or only coolant?

Three-ply silicone handles both. It's rated for pressure cycles and heat, so turbo boost lines and intercooler piping work fine. Just confirm the operating temperature and pressure range match your application.

Does this hose need any prep before installation?

No prep required. Slip it on, clamp it down, and route it. If you're installing it on a hot engine, let everything cool first for a secure fit.