I can answer some of your questions.
Is the project still alive? It's been 3 years since any update has been released. Earth has responded to an email i sent, but has not responded to a problem I posted on the message board. I wouldn't say it's TOTALLY dead, but it's not nearly as alive as it used to be.
The 4 alias names are your 4 in tradewars game names. When you play tradewars, you MUST use one of the 4 names listed, or ATTAC will not accept you as a registered player.
I am pretty sure I purchased ATTAC during version 3.xx and was given new codes for version 4.xx for free. As ATTAC hasn't been updated in 3 years, it is very possible that 4.11 is the final version of ATTAC, and therefore your registration will never expire.
The ATTAC you have will accept the new Reg codes you recieve when you purchase them
The code sent to you is useable on as many computers as you want. and you could run all the PCs at once.
While I still have and use ATTAC, the TW community reguards it as one of the not so good programs to use with tradewars. Before spending money, I would go to the tradewars forums http://www.classictw.com
and browse around to see what others are using and what seems best for you. If ATTAC still seems to be the best choice then enjoy.