Tiny-
First a happy new year to you! I have 29g DT with a 20g sump and have a 1/10th hp JBJ Arctica Chiller. If you go to the JBJ website they have a calculator that wi help determine the correct size chiller for your system. The calculator takes into account ambient temp, number and wattage of pumps/powerheads and desired temp.
As for recommended chillers the JBJ brand came highly recommended to me when I did my search a couple months ago.
I have mine plumbed in my return line, but when you do this know that your flow will be dramatically reduced. To maintain the same high flow rate I added a couple extra pumps-a K nano and a Rio 1100 return in addition to my Mag 5 return that goes through the chiller and my MP10 and K1 in the DT.