They say " hardy" but what is your actual growing zone compared to the recommended growing zone for this plant being offered. A hardy for this plant may be above your zone. Now that's something to be considered for in ground planting. As for growing in pots.....success in such a situation may be very dicey or a fail no matter what form this plant comes in below the belt if you are considering to do this outdoors instead of a greenhouse.

You can buy alstromeria growing in pots in garden centres later in the year, usually in flower. As for their hardiness, as Loosestrife intimates, they're not bone hardy, even in the ground - fine with down to -5, but lower than that for any significant period and they will be affected. In pots, they're even more vulnerable, so if you can provide winter protection when the weather turns arctic (sink the pots in the border and cover with fleece and keep your fingers crossed, or move to a frost free place) then any variety you fancy should be fine. Any bare root or bulb/rhizome purchased now would need potting up and keeping somewhere inside until end of May, or when risk of frost is past.

Yes, the "bulbs" have very little shelf life, and should be handled carefully, since breaking the tuberous roots off of the crowns is easily done, and a death sentence for the plants.