Shoutbox

1) This can't really be done because it can cause more problems if you mix up which account you are using to talk to a contact imo (like all of your accounts that are signed in might be talking to the same person and I can see some problems with people mixing it up).  I personally would prefer a way to differentiate between the different accounts rather than mixing them up even more. (just my opinion)

2) You can change the tool-tip (the ballon that comes up when you hover over the icon) with the use of the script in [Release] Email tooltip.  This i probably your best option, at least for the moment.

3) i) There i a script that can do that plus a lot more though there are some bugs with it at the moment, they aren't too bad.  The script can be found in Messenger Plus! Live Enhancer.

ii) Plus has not done this for a number of versions (if I remember rightlyit did it back ages ago) instead most people these days use the likesof mess patch from http://mess.be or a-patch to get rid of the ads andcustomise the look of their messenger further.

iii) Both the Patches I listed about can do this or you too.

I hope I have helped, if you need any more information, just ask