You will need a Garmin USB datacard programmer and a card.
The card reader/writer is proprietry Garmin ..... but here is a good reliable, cheap source
There are "generic" card suppliers that are a less than a genuine Garmin. They are excellent and the only difference is that instead of a pull out "lever" on the card used to remove it from the unit, these just have a loop of braid.
You didn't need to buy Mapsource: Its available as a download from Garmin.com
Did you consider the 298 with UK&I G2 charts preloaded ? I don't think they work our much more than without , unless you got a great bargain ... this wasn't available when I purchased my 292 >>>> but good old Garmin sent me one when I returned my old unit under warranty with a screen problem
Nice bit of kit : I've been very pleased with the 292