I'm F2P with the exception of one purchase of the Wargreymon pack. Started playing a couple of months ago or so. I'm level 128 and I have 5 digimon that are 4/4 Limit broken. I've got a bunch more that are not far from 4/4. I've also got 1.3MM bits, and gaining. The key to becoming powerful on this game quickly is actually to slow down, I think. Sometimes I can actually clear the events on hard, and that's without even using 9+2 combos or anything like that.
From what I've seen as far as the leveling, here are my thoughts.
- Levels 0 - 20: don't use any floppies here if you can access digimon with queen rarity (4) or higher. Fuse 5 at a time, and make sure it's the same color.
- Levels 20 - 30 ish: Use bronze floppy + 4 of same colored digimon
- Levels 30 - 45 ish: Use silver floppy + 4 of same colored digimon
- Levels 45+: Use gold floppy + 4 of same colored digimon
Once you get above level 20, I strongly recommend ONLY fusing when you are using floppies. I really think that's the key to gaining power quickly. Feels slow as shit, but if you do at least the daily every day, you gain at MINIMUM one gold, silver, and bronze floppy per day.
This has already been covered in other areas of this forum, but to REALLY get the most out of fusing, it's best to even fuse your material digimon up to level 10ish if possible before doing your real fusing with the floppies. This is super effective when you're using rarities of 5 and above. I can usually gold floppy + 4 digimon and cover 5 levels at a time up to level 70.