The AT835b is an oldie but a goody for the price.
Sound for picture is a tough gig at any time, but especially so on a micro budget. Lot's of folks are hot of the Zoom H4n (about US$300) although I was not impressed with the sound, but that may have been a problem with gain-staging, etc.
"Roomy" is that echoey sound you get in overly ambient spaces. Shotgun/lobar mics, because of the way they are designed and the laws of acoustics, tend to make the dialog recorded in "normal" rooms (kitchens, living rooms, etc.) sound like the are in an tiled bathroom.
The hum is another aspect of how technology can only do what it is designed to do, not what you want it to do. You ears/brain have a built-in "editing function" that allows you to ignore sounds you don't want to hear. A mic records only mono instead of 360 degrees like you do, so sounds of which you are not aware are greatly overemphasized; things like traffic, refrigerators, computers, dryers and other appliances... you get the idea. It could also be a problem with the audio recorder itself, or hum caused by the proximity of the audio recorder to an intense electrical field. (When I was a musician I played a club in a skyscraper in Manhattan where all of the electrical conduits for the entire building were directly behind the stage wall - HUM HELL!!!)
The playback system also plays a role - it can only reproduce stereo or at best 5.1 or 7.1 surround. I was privileged to listen to a demo of Charles Morrows 360 sound system, in essence a 14.2 system. It required a very complex mic/recorder system in the field and while very convincing it still required a lot of manipulation of the sounds to create the illusion.