I think on Spieth/Reed, they can send them out as a foursomes pairing and then break them up for four ball. Foursomes is the tougher one to match guys up, so leaving together a pair that has had success (1-1-2...should be 2-1-1 if not for the 4 up with 6 to play meltdown against Sergio and RCB) would make sense. Then they can send Reed out with Tiger in four ball and Spieth with his buddy JT.
If Tiger only plays 1 match a day, I’d keep him in four ball. He was #1 in strokes gained approach, let him hit stingers off the tee all day and then fire in at every flag instead of only hitting half the approach shots. The driver has been a lot better since he tweaked the shaft and loft, but this place doesn’t require driver off the tee. Maybe the JT pairing that had been talked about would work out, Tiger can put those stingers in play and then free up JT to be more aggressive with the big stick.
Fourballs are the first matches, and I don't see Spieth and Reed being broken up if they have success. In 2016, no U.S. team was was split up in their next match after a win except for Koepka/Sneds on Saturday, and that's just because Snedeker wasn't going to play two matches. I would say Spieth/JT is a plan B team, that only sees action of Reed/Spieth fail, and even then, Spieth may get sat depending on how that failure happened.
As for Tiger, I expect he'll play at least 4 matches unless he expressly asks out or plays terribly. If he's playing well, he's not going to let his age or injury history keep him out.
My predictions for the first fourball pairings are:
Spieth/Reed
Tiger/Bryson
Rickie/JT
Brooks/DJ
And if any of those teams win, they'll be back out for foursomes. I'm guessing Phil doesn't play Day 1.