The 820 is basically the same as our 890 without the third manual. I'd had more experience with Allen before we got this (used) Rodgers about a year ago, but quickly became a real fan of these 1980's analogs. I think you'll like it very much.
The controls are wonderful, the lighted drawknobs and lighted piston system. With the double memory and all those pistonsyou'll have plenty of registration storage. You might turn down the brightness of thedrawknob lamps as low as you can and still see them, as that will greatly reduce the frequency of burned-out lamps (and reduce the heat-lamp effect in the summer time!)
Any organ will sound a little sterile in a small church unless the acoustics are very live. You may want to experiment with speaker placement.Try bouncing the sound off a hard-surface wall oroff the ceiling before it gets to your ears. Also, the 2 + 1 speaker complement you mention is the bare minimum for that model. You might ask the dealer if he has any spare Rodgers cabinets (such as M10 or M6 column-style). Putting two on each manual channel and aiming them in different directions may help the organ sound better in your small room. (No need to double up the subwoofer!)
Our 890 has had few service problems, though as an organ technician myself I've simply fixed things as they cropped up. In your case you might want to be sure the dealer has a tech who knows and appreciates these organs and will be willing to take care of any issues that come up. Also be sure they tune it and do a careful voicing after they bring it in. These organs can sound very poor if the voicing is not done correctly. I've gone out on service calls and found them with the stops so badly out of balance that you couldn't even use some of them.
Good luck. Let us know how it turns out.