Type: You want a simple condensate hood with condensate channel (lip) and drain. Stainless looks better and more expensive, but galvanized is fine.
Size: You want a hood with a minimum of 6" overhang on front side, left side, and right side to fully capture all vapor/heat/GAS from kettle. No overhang required on rear side due to wall. Example, if cooking area is 30" x 30" (w/ rear wall), hood size should be 42" x 36". If island style, hood size should be 42" x 42".
CFM: You want to use the least amount of cfm that will do the job. No need to suck out costly AC or Heat from your home. A typical condensate hood will draw 150 to 400 cfm per linear foot of hood, depending on the location and application. If you can locate your brewing equipment in a corner of the room, and thus mount the hood in a corner, you can lower your cfm requirements. Also, as you decrease the distance between your cooking surface and the hood (vertical distance), the less cfm's you will need. I do not know if there is a code for the minimum height that a hood must be mounted above the finished floor in a home. For restaurants, code is 6'-6" or 6'-8", so the cooks don't bang there head on the hood. Lots of variable go into cfm calculations, but nothing difficult.
Make-up air: This could be accomplished by simply opening up a window that is close to your cooking area, or less simply by a second fan and duct work.
Fan Size: First, must know cfm needed at hood. Second, must know length of duct run. Third, must know duct size/diameter.
You should be able to find a used condensate hood for cheap at a used restaurant equipment dealer. If it is stainless, it will clean up nicely.