Great checklist! Here's our situation:
ISP service: Cable
ISP modem: stand alone, but there is a router in between the modem and the DIR-632. I set it up following the procedure to "Connect to Another Router" in the manual.
Modes: It was mixed b, g and n. I have now set it to mixed g and n.
Auto channel scan: Was on, I have now turned it off and set to channel 11.
Any other wifi: We're in a residential subdivision, so there are several other wifi setups in neighboring houses, but nothing closer than that.
Connected devices: We generally have at least two or three devices connected at once.
Cordless phones: There are a couple of Panasonic 5.8GHz phones in the house.
I'll let you know if it's more stable after the changes. Thanks!