Exactly, you can get an easy 1000 Rubies a week, and for that people that never tried it give it a change you can easily get to Platimum 1 or 2 and you don't even have to spend rubies to do so.
Here´s the gist, every day you get 3 chances to fight any more and you pay 10 rubies per extra fight, you can only use 1 figther per Match so lets say you go with Lady zero, Orochi and Gonuts, after that first match they are not selectable for the day even if you didn't use them so choose wisely.
Each Victory gives you points, points are based on health, time and victories. The perfect run is win all 3 fights with a single character under 30 seconds and a tolal CP of 70K or more and you get 125 points, 100 is the goal you should aim for and thats doable with low CP you just need to do it with One character.
The AI is not as aggressive here as opposed to League and all fights are 1 at the time. If you win all 3 fights for the whole week and the goal of 100 points you are guarantied to get to Platinum wich is getting 3000 points, forget about Diamond tho at that point you at looking at like 7K upwards in points and that is too much of an invesment in Rubies belive me I tried once.
Some tips and suggestions, it really doesn't matter what order you choose the important thing is making 1 character you main Nuke, One of my teams is Ryo 96 as the leader for his 50% Purple attack buff, Idol Kula as my Nuke and Igniz as my back up. Dont think the world is over if you dont get perfects or loose a character, the more CP you have the more leeway to fuck up and not loose as much remember 100 is the goal everything else is bonus points. The Ai will roll backwards 90% so account for that.