All of what you said plus arena. The simplest strategy in arena I think is to maintain a kage/super kage rank. That way you get another 4-5 seal scrolls a month. It's not that much, but they add up.
If you can go up to 6 paths every months than that's actually great. But it would mean much more hard work and nerves of steal. ;P;P;P

Also, depending on how strong you are (even as f2p you can be very strong and one of the top players on your server) you c*so get seal scrolls from sage battle. Positions 1-3 from each team get a seal scroll. So basically you need to be in top 9 (worse case scenario) in the sage battlefield. Which might not be all that hard. It's also possible to be 12th or 15th overall and be top 3 in one sage team if the respective team was much weaker than the rest. Whatever, you get the point.
You c*so get seal scrolls from matsuri challenge, 1 per challenge and a few frags if you manage to finish all five fights. But this also kinda depends on your luck, since the system might put you too many times against way stronger opponents.

I know the feeling bro. ;P;P;P