What overhead ? They're like $6 a piece. You could get six of them for $40. If they're I2C , that's four wires each with two of the wires connecting to the same pins on all six lcd and the same for the power wires. They're address based. You can get some LEXAN
sheet from TAP plastics on the Alemeda and get the rectangular holes cut out (either there or somewhere else) , drill and tap the mounting holes your self and build a control panel box with all your electronics in it and connectors on the side. If you don't want to mess with the job of epoxying the pieces together for the box you can use small cabinet L brackets from home depot and drill and tap the mounting holes . You can mount your 5V power supply , your arduino , all your electronics in the box and put a 120v AC Jack (like on a PC) for the power plug. You get power connector from Halted Specialty Surplus for the all the heater connections.
Are you going to seal your DS18B20's in EPOXY ?
Are you busing all the DS18B20's together ?
Have figured out how you're going to do the timers ?
This isn't the right section of the forum for timer questions because it is beyond the scope of Project Guidance so you might want to post a list of all the times in the Programming section . You can post in Mechanics and Power for help controlling the heaters.