.280-290, although flirting with .300+ is not impossible (just unlikely)
19-22 HR, 90 Runs, 80 RsBI and 0 SBs, plus 50+ doubles
If he gets another 425 ABs and hits .270 over those ABs, he'll finish the year at .286. If he hits .260 over those ABs, he'll finish .277. Given his career avg is .274, given he's moved into the AL, and given he's off to a torrid .350 start, I think he's well on his way to a .285ish season (with a 20% chance to do .300+)
His OPS right now is at a career high level, but that's driven by his doubles, not by his Homers, and will continue to be the case. Batting low in the order will hurt his counting stats, but he will hit 50+ doubles, and on a team that will score 900 odd runs, that will lead to impressive totals for a guy batting 7th. He's pretty valuable as a 2B in Yahoo, but not sure he's worthwhile in all leagues as a pure 3B. But I could certainly see him outperforming a guy like Huff who was drafted 5-15 rounds sooner (probably averaging what Huff has done the past couple seasons)
As for his HR, if he ends up with say, 20 HR, it wouldn't surprise me to see him have like 7 at the Break and 13 (or some similar imbalanced split) after the Break as he learns pitchers and parks better and gets cheapies from late season AAA pitchers.