Refer to the installing instruction with your Baro Damper, if a Field Controls RC type, go the their website, they have installation instructions online.
Please look here, been discussed numerous times. Must be no less then 18" from the stove, doesn't really matter where it's located, but "should" be in a straight section of pipe. Baro damper?
Yes, a Draft Gauge aka Manometer is the ONLY way to set the correct weight/draft on the stove. The weight shown on the baro is a close setting to get you started and some people just use it that way, but to really check it and calibrate correctly, a draft gauge is a must.