I don't know what the miniumum zoom is on google maps.. it may be that they simply dont supply zoom 1 or 0 for maps..

for me though there is more detail in zoom level 3 than zoom level 4.. but I wouldn't bother trying to download anything less than 3..

as for the Holux... I have the M-1200 and it does the same wondering around while stopped.. i have mapped the hardware "back" key on the nokia to start/stop GPS.. so it's easy to just switch off the gps when stopped.
As for sensitivity.. my Holux works fine even in my pocket while in the car.. and locks well inside my house. . I don't have any problem will weak signals with it.