Your welcome Samuel, the timer is probably a standard NE555, but if the one your using works, go for it!
The 2n2222 is rated for up to 500ma, so you should have no problem running 4 or 5 LEDs on each one. In theory, even if you run your LEDs at thier maximum rating of 50ma, you should be able to connect 10 of them to each transistor, allthough I imagine the transistor would run pretty hot!
Generally each LED would only be drawing around 20ma and the 2n2222 will have no problem handling 100ma.
I would still use the If/Then loop to poll the detectors every once in a while, and save the interrupts for more important things.

Dave