1.you need a hub that is make for a disc brake any model of shimano should work for you.you need to replace the hub,spokes ( may be different length ),can use the same rim. same for the rear,replace the hub.
2. your wheel would have 36 spokes not 34, or 32, but cruiser usually are 36.
3. if replacing these wheels with new hubs,spokes,disc for brakes will cost $250 & up.
4.best thing to do would be return the bike for a refund and buy the bike with the features you want.