Simple idea for how much ISO is needed.

mpqr7

A 4* requires around 365,821 + 12,500 = 378,321 ISO to champion when max covered. And you get to keep a 4* cover for 14 days.

So on average, a player who has non-championed, fully covered 4*s should be able to receive enough ISO to champ a fully covered 4* within 14 days. That way, if they receive their 14th cover, they can work hard and champion that character. Sure, if they receive two 14th covers, they won't be able to champion both, but at least they'd be able to champion one of them.

So that would be a total of 378,821 / 14 = 27,023 ISO per day. Preferably more around 30,000 ISO per day, as we need a bit extra for boosts during final pvp pushes.

Of course, if you want to give us more ISO per day, that would be great as well, seeing as many of us need millions to champion all our fully covered 4*s, but this would be a reasonable start.