Your plants should each end up 2'-3' tall (they are each medium sized pepper plants). Whether they need support depends on how close to each other you plant them. The quick rundown on spacing is that if you want to maximize the number of fruits per plant you give them more room (2' - 3'), but if you want to maximize the number of fruits per square foot in your garden you space them about 1 foot apart. The close spacing also allows the plants to support each other. If you go the 2' - 3' route you will need to stake or better-still cage the peppers.

Plant spacing is a hot topic here, and you will get some very good arguments. I grow lots of peppers and so space is premium in my garden. My beds are 4' wide and this year I am planting pairs of rows with 8 plants spaced 1' apart and then 2' between rows (config C):
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As for number of peppers, it will greatly depend on many many factors including soil, water, and fertilizing. Be warned that too much fertlizer can reduce the number of fruits.

The main thing is to relax and enjoy.

-John

Unclejohn said it well.
I have raised beds and use a spacing method similar to his "A" diagram except in rows of 3 not 4.
For my situation this works best. Once mature, the plants buffer one another from strong winds and also help support each other.

al_apeno, you didn't mention if you will be container gardening or planting directly into the ground.
Container gardening carries its own set of issues.
I put a few plants in containers each year and find that it's safer to stake them for insurance purposes if nothing else. Sometimes the wind can blow them enough to lean the plant toward one side of the pot loosening up the root ball, and a stable root system is important.
Containers need good drainage otherwise root rot will set in. Use an adequate size container or there will be an increased chance of the plant becoming root-bound.
I also find closer monitoring and more frequent watering is needed.

One slight advantage of containers is that the soil often becomes warmer earlier and stays warmer later in the season. This also becomes a dis-advantage in the heat of summer. Be careful not to over water chiles as they do not like their feet kept wet.
Some of the factors just mentioned can put stress on containered plants which many believe (including myself) yields hotter pods.

As unclejohn said, be cautious when fertilizing. Too frequent a fertilizing regiment may result in more foliage than pods.

If you live in the North those spacing will work. I lived in zone 9b and the spacing they showing will not yeild maxium amount of fruit.Plants in zones 9and 10 can get very large .So if you live in Zone 9-10 18" min.

Thanks for such thorough responses!

I plan on raising the plants in containers (probably in 12" pots), so it sounds like my best bet will be to use some sort of stake or cage around each plant.