Hello Muskrat,
If you haven't already done so, please see our trade tutorial at
http://www.tgft.org/tips.html.TA pulls all the data that the game will allow it to. This includes station sell prices of all items, whether you possess them or not, and station buy prices of anything that you possess at that station when you dock, either in storage or aboard your ship.
Station sell prices are static, and buy prices are dynamic. Buy prices change as players sell specific items at specific stations. It takes several hundred units of most commodities, but only a few units of most add-ons, to significantly affect buy prices. Depressed buy prices drift back upward over about a day or so if no further sales occur (of that item at that station). Buy prices normally will not change in the time it takes you to arrive at a station. Player trading activity isn't that intense.
Your #1 is correct.
On #3, buy prices are actually pretty stable most of the time, unless someone has sold a huge quantity of something within about a day after you last updated the price. So whether you use your stored TA data or the in-game optimum price pulled in space, you will usually get about the same result. My technique is to leave 1 unit in station storage every time I sell something. That way, I pull an up=to-date price for that item every time I dock at that station, and I'm always pretty well informed about the prices that I really care about, everywhere and all the time. The key is to do a lot of flying and docking.
Now imagine what would happen if a group of players had a system for sharing TA among themselves ... oh never mind ...
-- tsreknor