That seems like the best bet to me.  If this system is anything like Hattrick, expanding your arena is a waste of money.  Perhaps in this game it will be different, but until I start seeing sellouts on a regular basis, the one thing I don't want to do is expand an arena.  Improving the coach, seems like a rational first move however.  Perhaps I'll look into that.
Can someone tell me about this $50,000 newbie bonus?  Is that true?  If it is, how long can you expect to get free cash for?  When do you stop getting that bonus?