What Next?

I would install everything that I could. If you screw something up - he can paint it when he does the car. Brake and fuel lines. ebrake cables. Master cylinders for the brakes and clutch. Bleed them now if you can to avoid screw ups later. Trial fit anything that you can now, so that you are not risking dings later. I would hang the doors to get them fitting right. He can take them off for painting (or you can when delivered) so that they are aligned correctly.

Anything that to screw up now - he can paint when he does the car.

Mask off anything that you dont want overspray on!

Ensure that the front valance is prepped for paint on the inside also, It is visible when you pop the hood for shows!

No rubber installed anywhere. Consider having the windshield installed AFTER you have re-installed the dash - its a little easier IMHO, and the paint gets a chance to get harder.

Engine and tranny obviously - maybe not the radiator! Drive shaft now if you have the time and the car is up in the air.

Mask everything that you dont want paint on.

Rockers - they are low and painters will scimp on their efforts. Discuss how the car will get painted well down there.

Good luck - btw, Hawaii is over-rated.