well before i start the electronics, people should head over to
http://www.lsdiodes.com/ for .45cents a piece they have blue leds at about 5000mcd, they run on about 4.2 volts which is bit higher than you purchased but the price is so much better. i don't work for them, i just like getting deals.
the reason some people use 1 resistor, or a resistor on each led has alot to do with the power supply they are using or preference. if they are using 1 resistor, then they are just using it as a current limiting resistor, and should have the leds in series with each other. the theory behind that is, the resistor will trim the incoming voltage / current source, and make it suitable for the leds. this is done when they have actually have enough voltage for every led.
series or parallel hook ups - if you build the circuit with leds in series (one leg tied off the last led leg) the current will be locked between the leds (each led will receive the same current) but the voltage drops for each led can change. this is handy if your mixing leds that have different voltage requirements or a large supply (if each led needs 3volts, and you have 5leds, then you will need a combined voltage of 15volts for series) or you build the circuit with leds in parallel, where each led is tied leg by leg off the last. so they appear to be parallel. i can post a pic showing this if you need. the theory behind having leds in parrellal, voltage is locked across all the leds but current can change if needed between the leds. and the reason you see a resistor on each led is make sure its receiving the right current and partially for some protection. most people prefer parallel hook ups for leds projects, and usually it is to keep the project as cheap as possible and find a power supply that supplies just enough voltage to the led to turn on and the same voltage can turn on many leds.
resistor selection is dependent on the power supply used. i can give you the formulas or once you make up your mind on the voltage/current of the power supply i can do the math for you. and then you will have your answer. i would recommend finding a 5v dc transformer, or a 12v if nothing else. also a great place to find these is from an old cd player you don't use anymore, or some other small electronic consumer good you no longer need, or have a use for. i would just recommend you don't go over the 12v range unless your going to build in series.
photosensitive switches, are manufactured by a bunch of different companies, and all pretty much stick to a tried and true method. there isn't really any great benefit choosing one over the over, unless the cost difference is substantial.
i am a little confused
what do you mean by pod?
