Yes, unfortunately hexic.info is dead. The admins had pretty much abandoned it a while ago.
The best advice I can give you is patience. Nothing is forcing you to make moves, so double, triple, and quadruple check your moves before you pull the trigger. If for any reason you are not 100% confident that you will not cause a collapse, don't make a move. Hasty moves never got anyone this achievement.
As for multiplier farming, you MUST have a master grid, and it's advisable that you have it up in the first level before the stars begin to fall.