Nice setup Javajunkie!
I am growing a good deal of dragon fruit vines, I have many in 1 gal containers (keeping it that way until I move them to permanent spots). Physical Graffiti is one of the fastest growers for me and will multiply segments quite fast.
For those growing Dragon Fruit below zone 10a, I suggest you stay away from Selenicereus megalanthus. It did not flower until the fall and set fruit into the winter (which dropped off when we got a cold spike in the low 30s) Dragon fruit should overwinter inside fine, as long as its kept in a dry location with 4 hours or so of sunlight and temps above 30 degrees. Watering can be kept with a minimum especially if temps are below 60 (once every 2 weeks, or depending on medium moisture).
The fruit flowers and sets in the summer (around August). Depending on the selection it may fruit in late July to September (later if its Selenicereus megalanthus). The vines like high intensity filtered light in the majority of the plant with the top end of the vines reaching for full sun. If you have some humidity in the climate and temps are under 85 (don't worry to much about vine burn). Those in intense summer heat like AZ and TX, shade cloth might be a good idea. Don't be to shy with organic fertilizers during the long warm days of summer. Vines are receptive to foliar feeding at night especially feeding through the aerial roots.
You can get decent yields (from what I seen) in 10 to 15 gal containers. A porous well draining mix is optimal with 2-3 watering per week during hot days of summer. Once the vines get enough mass and are given some potassium flowering should commence in June.-July. I recommend that some of the watering cycles during the last phases of fruit development is withheld, so BRIX can increase and vines can use excess store of water and nutrients.