Did you try it on different PCs? Any anti-virus software running on your PC? Disconnect the cable plugged in WAN port of WR740N and leave your PC and LAN port for router connected. Default gateway...

WDR3600 is the main router and WR941ND is the WDS router, right? Have you ever tested the stability of WDR3600 when it is working alone? Change Channel width to 20MHz and fix a channel like 1. 6 or...

Maybe you can connect to Wi-Fi when the adapter is very close to main router if it has no antenna. But the router and adapter are not next to each to each normally, right? If you need adapters with...

No idea... Why not contact distributors in SG to confirm it? http://www.tp-link.sg/where-to-buy/?categoryid=901

No problem with your installation process? You can print when the printer is connected to your PC directly? http://www.tp-link.com/en/faq-242.html

There is a beta firmware to solve bandwidth control issue and it also works with Unifi. You have to ask for it from TP-LINK support team. http://ticket.tp-link.com/index.php?/Tickets/Submit