800ma max for the on board regulator.
You can provide power to the LEDs from an external supply.
To control 441 you'd probably want to use an 8x8 matrix IC and to use 7 of them
that would get you 448.
If each LED is drawing 20ma that's 8.96 AMPS, granted they will be strobing and you can dim them down but you need a pretty substantial power supply to drive them.
There is a practical limit to what the arduino can do. You can however design an 8x8 matrix and get it working as a proof of concept. Then use a barebones arduino that has only what you need to control a single matrix and use it to control each group of 64 LEDs. Then a master Arduino would tell them what to do and you would tell the master what to do using any number of inputs including a computer.