I can only answers some of your questions:
"If I purchase the AW-NU231 adapter can I use the tv as a computer monitor on my network with a tablet? I've heard IPAD works with certain tv's but not sure of 92840?"
No you cannot use your TV as a comptuer monitor by using the WiFi adapter. That adatper allows the VUDU Movies and VUDU apps to stream to your TV from your WiFi router, not your computer. VUDU is a type of internet delievered Video On Demand system. To connect your computer to your TV via WiFi, you should have DNLA in both the TV and your computer (without DNLA you would be very limited). The TV does not have DNLA software and you cannot add DNLA software to the TV.
The iPhone/iPad app for the TV does use the WiFi as well but the app is simply a touch screen remote control, not a method to transfer content from the iPhone/iPad to the TV.
You can directly connect your computer to the TV if your computer has HDMI output. Or if your computer has DVI output you can get a DVI-to-HDMI adapter cable. If your computer has DisplayPort output, there are DisplayPort-to-HDMI adatpers as well which would work. You should know in advance that since this is a projection TV (projects like a movie projector to the back of the screen) and not a direct view flat panel (like LCD or Plasma) there will be overscan. Overscan is when the projected image is slightly larger than the screen. This will cut off some of the computer picture if the computer is sending 1920 x 1080, preventing you from seeing some of the bottom control bar of a Windows desktop.. Overscan is on purpose to prevent the image from not filling the screen and to prevent the crap often found on the edges of cable signals from showing. Overscan on the TV cannot be removed, however many of the comptuer graphics cards can compensate and reduce the size of the image before sending it to the TV.
"With the warranty companies that offer service is anyone better than others? Do they cover the bulb if you go 4 years? Thinking about SquareTrade or Geek Squad."
I do not know a lot about the extended warranties available, however purchasing one just to cover the lamp is a bit of overkill. The replacement lamps cost $99 direclty from Mitsubishi. If you purchase an extended warranty, it should be for your peace of mind about the rest of the TV, not the lamp. Others can advise you about quality of extended warranties.
"Had an offer to buy a 92842 (2012) for $200.00 more than 92840 (2011). Have no plans for 3-D because I'm blind in one eye and 3-D doesn't work for me. What I've read says only difference is something with 3-D glasses."
There are more difference than the type of 3D glasses, however most of these are generational changes which are subtle and possibly not very important to you as an individual. These are also the type of changes that are almost impossible to list in spec sheets. Things like changes in some of the menu, changes in the way things are accessed, etc. While there may be improvements in the picture, both models can be made to look extermely good so it would be hard to say there are huge differences. Sometimes the changes are in the background to improve reliablity, ease of manufacture which helps reduce cost.