How to overcome the 21M limit of Bitcoins as adoption increases? Are there any ways to increase the Bitcoin maximum coin limit, as a wider adoption would mean there would be a lot of real money chasing fewer number of coins? Also can one hold a fraction of a coin?
A single Bitcoin is currently divisible up to 8 decimal places (giving you 21*10^14 units of money, or about 2.1 quadrillion units), nothing stops it from being divided further with small protocol change. In order to change the limit of Bitcoins created, one needs to change the protocol and force most of the Bitcoin network to adopt the change, which can be quite hard to do. This hard limit of the amount of Bitcoins is one of the features of the system, not a flaw - it is meant to fight against inflation. If for some reason you want a cryptocurrency without a limit (hint from Lohoris: you don't), try browsing for alternatives.

All in all, there will be enough Bitcoins to go around for everyone for a long while.