Henrietta

Everybody needs a hobby. And learning programming languages, believe or not, helps with maths. Mentioning your ability to program computers in resume would automagically make you all-around competent in computers. At least in non-technical bosses' eyes.

True. By so-very-negligible amounts, it's probably not worth to focus on it at all. Time costs, write yer code instead of counting your files.

Counting include files is a way to nowhere. Focus on your algorithms, DB schema and queries. Besides, there are plenty of accelerators around to help up with PHP itself.

Row-level locking in InnoDB may really prove useful and actually can provide a speed increase, as you don't need to lock whole tables during sensitive operations. Unless you don't care about locking at all :D

Try to code some sort of logging system, to log down bugs which can appear during normal usage of the game along with any trackbacks you can get. That might prove to be very useful if users start reporting lags or glitches.