Do these attach to my factory roof rails, or do I need additional hardware?

These mount directly to your factory roof rails. You'll need to verify your roof rail setup matches the standard attachment points — some crossbars use clamp-style mounts, others use key-locking systems. Test-fit the bars against your rails before finalizing installation.

What weight can these bars hold?

Maximum load capacity depends on your vehicle's roof rating and how the bars are secured to your rails. Check your owner's manual for your Highlander's roof weight limit, then distribute cargo evenly across both bars.

Can I paint these, or do they need prep work?

The anodized finish is designed to stay as-is. If you want to paint them, light sanding will help adhesion — but the factory finish is durable enough to skip that step unless you're matching a specific color.