great to see imp going cellular ! Badly needed as sim cards were biggest problem with legacy devices.
On the usb host in impc001, can we plug in wifi dongle here to get wifi ?
No, the Wifi support - which is scheduled for release 42 - uses an external single band or dual band wifi module connected via SDIO (it will also support BLE in those modules, just as it does on imp004m).
More details are in the datasheet. Your USB host port remains free for application use.