You have a number of things missing here, some easy (pull up resistors on your encoders and start stop switch, current limiting resistors on your rgb led) some more difficult (high current switching for your UV LEDs and heater and a motor controller for your fan.) It also looks like your 12 V power supply is too low in current capacity, the UV leds alone want 2 A the fan will want an unknown but non zero amount and the Arduino will want a couple of hundred ma or so and the heater wants an unknown but probably large (as in an additional 800ma or so ) of power at 12V so the original article's 5A 12V supply is probably more reasonable. For breadboarding a dual 1.5 or 2 amp motor driver would do for your fan and heater, it may be a little small for your LEDs (since it is desirable to not be running at a devices maximum current rating). There are cheapish 6A single channel motor drivers available from Ebay (I have a URL if you need one). This probably isn't ideal for a PCB design later though, for that you likely want power MOSFETs which may need heat sinks.
(edit: I forgot the 600MA for your stepper motor in the current calculation so
.5A arduino + 2A UV leds + .6A stepper .8A heater + .12 A fan = 4A@12v
so a 5A 12v power supply is probably correct. As well as you are possibly already aware, you shouldn't look at the UV leds when they are running as UV can damage your eyes.
Peter
