Those plants will grow 14+ft if you let them but the size of the tomatoes will start to get smaller if you let them grow that long. Always better to start up new plants and as they start to get almost to flowering stage clip the tops off the old plants and disconnect them from the reservoir. Just pour regular water with a little bit of dissolved epsom salt into the bucket twice daily early am and at sundown so the tomatoes still on the plant can ripen until the last plant. As you do this start feeding the new plants the reservoir
nutrients. By the time the last tomato is pluck from old plants the new plants will already have tomatoes forming. Try to keep a log of how long the plants disconnected from reservoir lasts for and how long it takes new plant to start forming tomatoes so you can adjust the timing for both so tomato production never stops.
Very nice setup with the rails. Let me know how it works out for you since you will have 1/4 inch of still water at the bottom of each rail. My rails completely drain so the roots get plenty air in between watering.