You can grow almost anything that will adapt to your growing conditions (cultural) in containers that size, but eventually, you'll need to change the soil & prune the roots to prevent a steady decline of whatever you decide to plant. I wish I could offer some suggestions for plant material suitable to the heat you will be growing in, but I don't know enough about material that tolerates the high root temperatures.

Moisture evaporating from the soil will cool roots considerably, but if you place a dark container in full sun, root temperatures could easily reach 130* F. or higher. I would just say that shading the containers, selecting white or a pastel as the container color, or using a cache pot (this is a second, larger container than your plant is in. You fill the bottom of the cache pot with coarse gravel so your container sits at an appropriate height. Then, fill the area surrounding your plant's container with more gravel & keep it moist. This arrangement both shades your container, and cools the whole arrangement as water evaporates from the gravel in the cache pot.

Choice of container size is directly related to the size of the plants root mass or the speed with which the soil drains. You can grow small plants in large pots without problems if the soil drains very well. Generally speaking though, you should select a container a little larger than the roots that is of a size that requires you to water daily or every other day. You can always use the cache pot technique & keep potting up until the plant reaches a size appropriate for the container you have ultimately selected as its home.

Azaleas are normally a plant with shallow roots. The reason for this is they are very particular that their roots are situated where aeration is highest - at the soil surface. Azalea's roots will colonize the entire container if soil is well aerated. They do not tolerate a soil that retains a saturated layer at the container's bottom. The roots rot at the interface between soggy & aerated soil, so choose an open soil or add drainage material to the soil. They are also fussy about high soil pH. Use an acid forming fertilizer (like Miracid) and water with rain water if possible. Adding a tsp of regular vinegar to your water is good, but not as good as rainwater when available.

Al