Handling current through a 74HC595

Hello,
apologies if this question is very stupid. :)
I have been toying with electronics for a little while, but I know I
lack some basic knowledge to wrap everything up together so... here is
my doubt.

I am designing some Christmas decoration with a bunch of LEDs driven by
an array of 74HC595s (controlled by an ATtiny45). The whole thing will be

I did something similar in the past, using three 595s to control three
7-segment LED displays, but I did it fairly randomly: I just connected
each output to each segment, with a resistor between the two.
Since this thing I'm planning to do is going to be simple yet much
bigger -- involving twelve 595s -- I'd like to do things properly.
The 96 LEDs could and probably will be all on at some point, so
considering a current draw of 15 mA for each LED, the whole thing would
draw a total of about 15 A, which is pretty much impossible to handle.
Correct? I will probably have to investigate charlieplexing to such a
big scale, or maybe make it so the 595s are working one by one at a fast
rate (by pushing a series of logic zeros down the data line).

In any case, let's assume for the sake of the example that I want to be
able to drive eight LEDs with a single 595. The data*** tells me that
the maximum current load on each output pin is 35 mA, and the current
load on the supply pins (Vcc and ground) is 70 mA. I am not sure how to
interpret this: does it mean that the sum of the output currents can't
be more than 70 mA?
If that is the case, I suppose that I could use transistors. Would
connecting each output to the base of an NPN and the LED (with a series
resistor) between Vcc and the emitter work?

Also, I'd like to finally understand whether it's better to source
current from a pin or sink current into a pin. I would think that
sourcing is "cleaner" because one doesn't "overdo" the chip -- if the
current is not enough, it simply doesn't work -- but I'm not sure about
that at all, because on many schematics I have seen LEDs sinking into
MCUs' ports.

Thank you in advance, and apologies again if I sound like an airhead. :D
When it comes to these things, well... I am!
--
Jollino (un vecchio gilet linguista internazionale)
I miei fotolibri: http://www.nicolucci.eu/ (Glimpses + Burgo Chieti)
.

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