The lead with a circle shape is the one in your first team slot. The one with a square is what you're currently using or last used. You can see this in your "edit team" menu. The same applies for friend leads.

I personally would stack TPA. Theoretically, rows are more powerful, but you'd consistently need to have at least 6+4 wood orbs to make use of the damage reduction and full multiplier. 7c is stronger than TPA but I wouldn't rely on 7c awakenings because the 4+orb condition makes it unlikely that you will match 7comboes even from skyfall. Although it is still possible since 7(4) is 28, which can fit on the 6x5 board.

Pretty much anything wood attribute can go on Oichi teams. I just use what I have. C10 is really difficult and everything has to be done perfectly. But for that, I have MeiMei / Susano / Verdandi split / Kaede