......yyyyyyeah, sorry, not going to be able to open up with cuteness on this one.
Because for Firuthi it depends on the level of seriousness of the setting. He actually doesn't bother with coffee or stimulants much, but this is more for the sake of argument.
In casual settings or settings where powers aren't involved, he's just so plain jittery he doesn't have to sleep for days.
In more serious settings that have to worry about powers? That much caffeine, especially when you add cream and sugar to the mix, runs the risk of turning him into a very cranky eldritch abomination. If he's under extreme stress and that much coffee, it's practically guaranteed.
Matt: "You kiddin' me? I work for the railroad. 5 cups in the mornin', and five cups in the afternoon if it's cold outside or things just aren't goin' my way."
(I don't know why my fursona is suddenly an Italian from Brooklynn, but for real, since my fursona and I basically one in the same, he'd probably be super focused and super wound up for a couple hours, and then have a massive caffiene withdrawl crash and pass out somewhere)
Would be just fine... the "crash", however would be "Biblical" as the entirety of the known Internet of planet Earth would go off line, from the DOS that would ensue, as he <is> the main server platform.