As I know, MA180 and MA260 are 3G modems but M5360 is not.

I don't think your problem is the same as it works sometimes. You'd better describe it in details here or start a new thread. When it disconnects, can you access the server with http://WAN IP:port?...

Who is your internet provider? Before set it up, how about status of ADSL light on D2? Is it solid on? Did you get configuration details like VPI, VCI, connection type/encapsulation mode, username...

Yours is V1? What kinds of Wi-Fi problem?

How about upgrading the firmware? You tried g.dmt? If it won't help, check the replacement procedure in India here. http://www.tp-link.in/support/rma/

The printer cannot obtain IP address automatically as the windows, mac etc.? If so, why not change IP settings on the printer directly? On web interface of D2, go to DHCP Server---Address Reservation...