Amaryllis can be planted in a small pot (not much larger than the bulb) 4 X 4 Is big enough for 24 cm Cir bulbs.  You want about ½ an inch to an inch between the bulb and the edge of the pot.

Plant your amaryllis with part of the bulb out of the soil.  In fact, in pots sometimes the whole bulb is above the soil, so that the roots can have more soil under the bulb to grow into. This can make the bulb topple over if it is not fully rooted when the bulb blooms, so be sure you tamp the soil down really well.  This also prevents water from getting into the neck of the bulb easily.  Water well after planting and then water only after the soil starts to dry out.  Once every week or so should be enough. Under watering is better than over watering. Usually I plant them outside after they are done blooming for the first time, but we live in Arizona so if you have frost you will need to keep your plant inside or in a protected area so the bulb doesn't freeze.  They are very drought and heat resistant and will re-bloom naturally in the spring once they are established.