Capuano, 32, has spent most of his career with the Brewers and has very good control and a decent strikeout rate for a lefty. He had Tommy John surgery a few years ago and missed the 2008 and 2009 seasons. You can read much more about him in Chris's article from last week.
Buchholz turned 29 in October and is perhaps best known for having been swapped to the Astros when the Phillies acquired Billy Wagner prior to the 2004 season. Buchholz also had Tommy John surgery, his in 2009, and appeared in nine games with the Rockies and Blue Jays in 2010.
Contract values have not yet been disclosed, but I suspect both are low-base, high-incentive deals with Capuano's deal likely to be higher than Buchholz's based on past performance. I'll also predict that Capuano has some assurance that he'll be in the starting rotation since that's precisely what led to his talks with the Brewers falling apart last week.
Igarashi was awful last year and will not be missed. He is due to make $1.75 million this season, so wherever he winds up the Mets will be responsible for that amount less the league minimum salary, assuming he doesn't come back to the Mets. If he goes unclaimed then the Mets will have a very expensive minor league bullpen arm.