Azaleas do excellent in pots, as long as you don't let them dry out. Use an ericaceous compost and feed. The pot size should be about 10-15 cm larger than the pot you buy them in, changed up by the same amount every year or two until it gets the size you want it to be. That should be a minimum of 50 cm wide and tall for medium-sized hybrids, 25 cm for dwarfs, and a meter or more for the bigger deciduous types. If you are going to keep them over the winter, select the varieties for hardiness, wrap the pots in bubble wrap over the winter, and keep them in a sheltered spot then.