Yes, galvanized metal can off gas some dangerous fumes when heated, it's called zinc poisoning. Not sure if it will get hot enough in your smoker, but why take a chance? Bare steel, stainless or brass chains would be OK though.
Use the search function on the side to look at info on PID controllers. Basically it's a little computer control that you set a desired "set point" to cook at (say 225*) and the controller will provide power to your electric element as needed to maintain that set point. A normal setup included the PID controller, the temperature probe, and some sort of relay to control the heat source. Most people use a SSR (Solid State Relay) which is an electronic switch. It takes the low amperage, low voltage output from the PID to switch a larger amperage & voltage load on and off (ie, your heating element).
Auberins makes models that are very popular here. They have parts to build your own, and pre-made control modules.
here is a pre-made model that would run one of your 1,000 watt elements or the 1,500 watt brinkmann element. If you want to run both of your elements, you will have to build something as I don't think they have an off the shelf ready to run module for 2,000 watts or more (and you would want it rated a little higher than the maximum load).
Before I would spend the money on the prebuilt model, I would take one of those 1,000 watt elements out of the housing and run it straight (ie, hard wired to 120v so it's on 100% of the time when plugged in). Let this sit in the cabinet and see what sort of temps you get. If you are not happy with the output, then add the 2nd 1,000 watt element and run them. I would think the two will output more heat than you want/need and the best mix is between them. There are a lot of fridge conversions on this site that use the use the 1,500 watt brinkmann element and many of those appear to have more interior volume than your smoker does in the photos. So I'm fairly certain that element would work for you if you need more than 1,000 watts.
If you want to use both of the 1,000 watt elements you have now, then you have to build a custom PID to run both your elements. It's not hard to do, but you will be working with electricity and if not done right, well it could be dangerous.