greetings hesterrp - the stainless steel collector plate is a good idea and should work fine until it reaches the same temperature, or close to, the same temperature as the steam rising from the brew kettle. After which, the steam will simply deflect off the sheet defeating your purpose.
The cheapest way to assure good ventilation is to simply use a fan to stratify the air and open a window or crack open the door(s). That said, if you choose to use an exhaust fan to remove the air from the space, you will need to crack open a door or window anyway. You see, you can?t remove air from a space without replacing it with air from some other place outside the space you?re exhausting from. Exhausting without replacing would cause the space to be drawn into a negative pressure and within a very short time period, the exhaust will continue to run, but will stop moving air completely.
Just a point to consider if you choose to mechanically exhaust your brewing area.