Current Limiting Resistors for Multi-Branch LED circuit
Well, first, having just one big resistor will work the same as several small resistors. Next, parallel leds need more current (bigger batteries and lower value resistors) while series strings need more voltage (higher voltage batteries and higher value resistors) so you're going to have to decide there as you could go either way. You'll need to know what voltages your leds need and get a battery slightly higher than that (the closer you can get the led - or led string - voltage to your battery voltage, the less energy gets burned off as heat in the resistor). E.g. a bunch of parallel 2.3V leds could be run of a 3V battery with only a small resistor, while a series string of 3x2.3V leds would need a battery of 7.5V or more (5x1.5V) but may still only need a small resistor as the voltage of the led string is still only a little bit lower than the battery voltage. just be aware, not all leds are created equal, some red leds only need 1.5V or so to run, greens can be 2-3V, blues and whites can be 3-4V and some uv leds need over 5V, so just keep in mind that what works with one led might not work with another (3x1.5V leds need 4.5V but so might a 1.5V led in series with a 3V led). Thankfully there are lots of led resistor calculators on the internet to help you out.