Will this hose work for coolant, vacuum, and boost lines?

Yes. Three-ply silicone handles all three applications without degradation. Just confirm your line pressure is within silicone's rated range before installation.

Do I need hose clamps?

Hose clamps are not included with this segment. You'll need two clamps (one for each end) sized to your 3.00" diameter tubing — typically T-bolt or band-style clamps rated for the application.

Can I use this as a repair patch on a cracked stock hose?

This is a straight segment designed for full-line replacement or custom routing. If you're patching a split, you'll need a coupling sleeve or splice fitting to join it to existing hose — not included here.