Setting filters will not help you to avoid dust. During the operation of the cooling fans, the blades friction against the air. This leads to the magnetization. All the dust from the premises will be there. Remember the screens of old TVs? They were always in the dust. I recommend you not to restrict air flow into the room. Use a vacuum cleaner more often.
Positive pressure of FILTERED air in the room will reduce dust levels quite a bit.
It's not a 100% cure, but it's a LOT better than nothing.
It's also nice if you live in an area that gets smoke at times (last summer in Central Washington was BAD) to be able to BREATH.
The "increase filter area" idea is a sensible one - it's one of the reasons most large commercial installations use 4" filers, they have that "V" built into them.
Better yet, make it a 4 or 5 sided "box" of filters on the intake (4 if the fan is against the floor, a wall, or the ceiling, 5 otherwise).