Firstly, try roasting without all of the "extra confusing bits" *(DMM, thermocouple, etc.), this will aid in learning the sensory aspects (sounds, smells) of the roast process.
General precautions: 1) Try to use in a well-ventilated area; you will smoke up your kitchen if you dont have a ducted hood. *2) Without some sort of chaff collection, you will make a mess, even with a small batch. *3) things will get hot, so make sure you have some sort of gloves etc. on hand so you dont get burnt.
For the chimney, just cut the bottom of the tin off, using your standard side-cutting can opener. *Using some sharp kitchen shears, cut a single slit about a third to halfway up the side of the tin. *Using gloves, gently squeeze the tin to allow the two now separate parts of the tin to overlap and insert (about 4 cm deep) into the "roasting chamber" of the crazy popper.
For a chaff collector, get a hold of some metal flyscreen, and cut down to approx. 30cm x 30cm square. *Using gloves, roll the square into a cylinder shape slightly bigger than the tin (chimney). *Then close off one end, and bend cylinder to a 90 degree elbow. *This creates a small "well" to catch the chaff during the roast. *Slide the cylinder over the tin, squeezing a bit to constrict the cylinder above the top of the tin (helps keep chaff from falling between the tin/collector) and you have a chaff collector.
Starting batch size: Id start at say 100g. *From there, you can increase the batch size by 10 grams each roast until your popper hits thermal cutout. *You just then back off 10 grams or so until the roast completes without cutting out.
Roast level: Familiarise yourself with the entire roast process. *Observe what happens before first crack, during first crack, before second crack and during second crack. *Poppers roast quickly, so you might only get a minute or two between first crack and second crack, if youre lucky. *After youve gotten used to roasting, then add things like a datalogger etc.
For cooling, a cookie sheet and fan are all you really need for small popper roasts. *No real need for elaborate cooling apparatus.