Here is a link for you: http://www.tp-link.com/en/article/?faqid=449

I don't think this router supports the bandwidth control.

have no idea. why not contact the tp-link guys for help?

As far as i know, the OID info should be from the third party SNMP management software with public MIB.

Try the connection mode as " Always on" and do not click on "connect". Then check whether you have 3G IP address on the status page.

All the adapters will share the bandwidth. The more adapters you have, the slower speed you get. I found a link here and hope it will help you: http://www.tp-link.com/en/article/?faqid=409