How many LED's can you power off one 555 timer?
As many as you need or want to.
Also if you wanted more LED's flash off the 555 timer would you just hook positive/positive and negative/negative of a LED to one and other to power them?
You mean placing them in series?
Yes, that will work up to a point (that point is when the sum of the forward voltages gets too high (when it approaches the supply voltage). Note that because the same current flows through all the LEDs, you can operate (say) three LEDs at 20mA, drawing only 20mA from the 555's output.
At that point you can place another string of LEDs in parallel with the first (with its own resistor). You can keep doing this until the total current drawn gets too high for the 555 to supply.
If you need more current, you use the 555 to switch one or more transistors that can each handle higher current than the 555. Using this approach you can keep going until you reach the limit of your power supply.
would you need add more capacitors and resistors and stuff to the timer if you want power more than one LED off the timer?
If you place them in series, only 1 resistor is required per string of LEDs. As you introduce more strings, more resistors are required (1 per string).
In general, you're not going to need more capacitors. But you may require some transistors and resistors to drive a large number of LEDs.
