Do I need hose clamps, or are they included?

Clamps aren't included with this hose. You'll need two worm-gear or band-style clamps rated for silicone — one for the 2.50" side and one for the 3.00" side. Size them according to your clamp manufacturer's specs.

Can I use this on a coolant system, or is it boost-only?

This works on both. 3-ply silicone handles coolant temperatures and boost pressure equally well. Make sure your clamps are also rated for your specific fluid and heat range to avoid leaks.

Will this fit my intake pipe, or do I need an adapter?

Test-fit your existing 2.50" and 3.00" diameter tubes first. If they're hose-barb style, this reducer slides on directly. If they're tubing with different wall thicknesses or custom diameters, you may need stepped barbs or adapters — measure before ordering.