Russ, read the article as below. Is it what you are trying to fulfill? http://www.tp-link.com/en/faq-715.html You got multiple internet connections and you can access internet when PC is connection...

The server is connected to WR740N by a switch? If so, the IP address should be assgined by WR740N and it is a private IP. I'm really confused about what you said...

If there is no problem with your upgrade process(right firmware, wired connection, no power cut-off), why not ask for a replacement under warranty?

When Android Wi-Fi is off but 3G on, actually you are access FTP server remotely from an external network. Did you use ftp://WAN IP to access it? WAN IP should be public.

In factory default settings, TD-8817 is working in bridge mode. Why do you want to enable it? There is another router to work with it?

Hardware version is V1? If so, you have to ugprade firmware for V1 instead of V2.