What certifications are required?

Set per trip by the operator. Advanced Nitrox and Decompression Procedures (or equivalent) is the usual floor. Trips past 150 feet want Trimix; overhead trips want Full Cave or Advanced Wreck. Recent experience in that configuration matters as much as the card.

Not everywhere. Ask before you book and expect to pay per cubic foot. Some remote operators need weeks of notice for a helium delivery.

Can a recreational buddy come?

On some trips, yes, on the same boat with a separate guide and profile. On expedition-style trips, no. Ask before you plan a shared holiday around it.

Technical Dive Trips: Deco, Deep, and Overhead

You plan the dive, run the deco, and carry your own bailout. What you need from a trip is an operator with the fills, the stage racks, the support boat, and the emergency plan to match. That is what these trips are.