I've never played him before, but talked to a few people to scout and here's what I found:
1. Stands over on the backhand side. Can rip 1 handed backhand, but in matches usually slices
2. Hits forehand with heavy topspin
3. Powerful 1st serve, powder puff 2nd
4. Terrible volleys
5. If you leave the ball high/short he can put it away easily
6. Has trouble with high balls, esp on backhand side.
7. He's in bad shape and gets tired by the 2nd set
I have a steady backhand when I have rhythm. I hit better cross-court and have trouble with consistency when I try to hit a winner down the line. On the run or in trouble it tends to fall short.
My forehand is my weapon and I can hit heavy topspin angles when I have time. Again big hitters I can get jammed. I have slightly above average volleys, a decent slice.
My serve is the big question mark. In practice it's about average. Flat/slice 1st, kick 2nd. In practice I'll double fault maybe once a set. I don't play many matches and haven't played a tournament like this in over a year. When I get nervous in matches my serve can completely fall apart and spray all over the court. I've double faulted whole games. I can't replicate what falls apart in practice as I usually serve really well in a lesson. I played sets 3 days last week and have been serving well, but I have no clue was will happen when I get nervous.
So what should my game plan be again him?
If he is as out of shape as you claim him to be, you should have no problem beating this guy with the right strategy. You should focus on winning the war (the match) rather than battles (individual points). In set 1 play very conservative. Focus on keeping the ball in play and extending rallies. Move him side to side as best as you can. If he slices you a short backhand you should try to hit a drop shot and get to net as quickly as you can. Not only will this tire him, it should give you a good shot at beating him if your volleys are better than his. If you don't feel comfortable running in after you hit drop shots, just hit the deepest lobs you can. I am a big guy myself and hate to chase down lobs that I can't smash. It resets the point and the energy required to go from the baseline to the net and then back to the baseline is enormous. Do not try and hit winners off his serve in set 1, even if you end up seeing a 2nd serve (unless you have break point or something) just focus on keeping the ball deep and making him rally with you. If he slows down during set 2, you should be slightly more aggressive as he will likely produce more errors when he gets tired.
Do not sit on changeovers. This is a psychological tactic and will make it seem like you aren't tired and can play all day with the same level of energy.
The receiver must play at the server's pace (within reason). Take as little time as possible between points. This will accelerate the rate at which he tires because he will have less time to recover after each point.
Hit with plenty of clearance over the net. You want to extend points and hitting the ball into the net will do you no good.