Tej, sounds cool....I was also considering to use arduino but the no. of I/O would have meant using at least two, and yes I did consider the mega. To go wireless I might use Xbee modules as the seem simple enough to use and multiple xbees can be used in one netwrork.
To control the system I'm using 8051 microprocessors, the coding is fairly simple, just treat each one as an up/down counter.....think it might be cheaper than arduino too.
Also instead of purchasing actual seven segments, ever considered buy the led strips and building it yourself. It maybe a bit more tedious and you'll save a lot more money.
Let me know how it goes and get some pics up when you're done. Best of luck