Most don't use the diff drop because of the slight negative CV angle at stock height, while others use it just in case. Most will tell you to save your money
You may want to get the trim packer for the driver's side lean if you go with the OME suspension, but otherwise you shouldn't need one.
Eventually you'll probably want to get new rear sway bar endlinks as it takes some stress off the rear sway bar when lifted and (for me at least) makes the rear end travel a little more freely because the sway bar isn't in a bind. You can get them from WabFab (where I got mine) or Medic83 on toyota120.com. You may also need new upper control arms if the alignment shops have trouble getting the front end straight after the lift. Depending on tire size there may be a few more things to consider.
The install time depends on a lot of factors, but I think it would be fair to say 4-8 hours depending on those factors. DIY or not depends on how comfortable you are; when I got my 4R I had never installed a suspension lift, now I have installed 6 or 7 for myself and others. I learned this by reading the writeups here and on toyota120.com, one of the most helpful writeups was Ark_Swamp_Rider's writeup (
http://www.toyota-4runner.org/4th-gen-t4rs/63618-finally-done-lift-tires.html) that featured a few
very helpful writeup links.
You're welcome, welcome to the forum! Most of us are nice but a lot of guys get fed up with the same question being asked repeatedly and this is a common one. Apparently a lot of these people have never been "newbs" to a forum, working on their vehicles, or any other thing for that matter.
I thought your name was Sandy, Sandy Tires. This is very confusing.