I have roasted in a popcorn popper. It takes about 4 minutes to roast a batch, but you cannot roast a lot of beans in a pop corn popper. The Gene cafe at the temperature setting I am using takes about 16 minutes.
Yes, the darker the roast, the more the sugar flavors come out. lighter roasts are usually more fruity or citrus tasting. This roast is not very dark because the oils are not coming out of the beans yet. Sweet Marias will let you know how dark you can roast the beans. Not many coffee beans can take an espresso roast.
Sumatra Mandheling has earthy flavors and sometimes tastes smokey. I like it but it is not my favorite.
I must say your set up is great.. One of our Arizona neighbors @maddbaggins brews beer, now we are thinking of doing it. I think we found all the equipment we need from a friend.. He would show us his weekly brew... Yum