4)let experienced players who know JAVA program extra play rules for the cards (at least level10s probably but I doubt we can be picky here?)
Although this will probably lead to thousands of lines of ugly code and more bugs it's the most feasible option to improve the simulator in the near future. This will of course require me to make the code available to the public which I'm still pondering about... What platform would you suggest if I decide to do that (I have no experience with open source)
sourceforge.net and github are the most common. Sourceforge is easier unless you are already familiar with git.
You choose who has access to change the code directly. Normally other people will submit patches to one of the people with commit access. That is how code quality is maintained, and tests.
As to license
if you don't care that someone changes the code and never gives you those changes even if they are selling it: Apache License or BSD
If you want the code to be distributed if someone distributes binaries: GPL
If you are worried that someone will turn you program into a web service and not release the code: AGPL 3.0
