I have an XDm-45 3.8 compact and an XD-45 compact . Both nice pistols but I'd recommended the 3.8. Adjustable grip and a better trigger. It's also a bit smaller than the XD if you're planning to carry it.
As for magazines, the standard 13 round mags will fit. The 3.8 package will come with one and a 9 round. It'll come with sleeves that turn the 13 Rounders into an extended flush fit.
The 3.8 package is really nice. The pistol, a 9 round mag, a 13 round mag, mag loader, holster and spare mag carrier.