I've had good results with both Bosch and Denso plugs in my 850 turbo. Regular copper plugs seem to work better in these engines than expensive plugs.
Especially in Florida weather, I'd use a 40 wt, either 15W-40 or 5W-40. If he drives hard, use the synthetic 5W-40 for sure. 5000 miles is a good oil drain interval, and MANN oil filters are excellent and about $4.
These transmissions need regular fluid changes. Any Dexron-III ATF is fine, and synthetic gives longer fluid life.
I'd use Auto-Rx to clean the engine (double treatment), transmission, and power steering.
Be sure he flushes and renews the brake fluid every two years in Florida humidity, and that he uses a DOT4+ brake fluid. It doesn't cost much from a Volvo dealership, or ATE fluid works very well. The timing belt is due at 70,000 or 5-years, I think--check this.
Volvospeed.com has excellent info.
Ken