You sure can.
http://www.campway.com/products/snugtop/xuv/index.html
http://www.campway.com/products/snugtop/xuv/pictures/silver-avalance-shell-low.jpg
Yes it will bolt right on.
5W30 weight.
You can get the no-skid mats to put under a throw rug (2' X3', $3 at Big Lots) and put it under the top of your mattress topper. I put it under my husband's side of the bed, since he scoots on and off - and moves the topper more.
I have 33 in on stock 05 1500 avalanche rubs little when turned hard but work & look awesome.
Donkey kong
The brake fluid on a 2003 Avalanche goes into the fluid reservoir. The reservoir should be bolted onto the drivers side of the firewall.
i have had 1800 pounds of sack-crete in the bed
Yes, But it won't look right. 1988 is when chevy redesigned the body / changed it.
Yes to 1500 only
under the rear seat pass. side. jack goes in and tighten(jack up) slightly to hold in place
with a lift i have seen 44s but with out a lift... no idea just run with the stock size as you will get better fuel economy
There are a bunch of different manufacturers of truck bed toppers or truck bed caps, as they are sometimes called. If you are looking for a new topper I've put a link in the related links for an info page that should help. If you're looking for a used topper I'd call the manufacturer of the kind of used topper you are interested in and ask them what other tacoma model/yr toppers are compatible with yours. It might take a little while and a couple of phone calls, but it's a lot easier than trying to retrofit a topper that doesn't fit your tacoma to begin with.