I had to actually record a final run of the last level so I can get enough gold to buy the final upgrades, due to an issue. For some reason, if you purchase extra slots for the item upgrades and after a run, one of the slots remains empty, the game will crash after the stage is completed. So in that regard, to get a 100% file, you just need to save enough gold to buy all the upgrades at once, thus, preventing the crash by not playing any levels afterwards.
I don't know if there is a cap to the stats. Given that the numbers go out of the boxes, after you reach a triple digit number, makes me believe that they are either unlimited or capped maybe at most at 999? I didn't bother to research further as it seems kind of pointless, given that you end up 1- shot busting any enemy at around 150+ stats. I guess it would be amusing to see a big damage number (or critical hit), but I am quite satisfied with the save file as it is currently.