If you are still low power don't spend coupons on ninja, save 20k and spend for power on fuko and hope the free ninja helps. By the time you are getting too decent power level, the meta will be completely different anyway.

If you are going to spend ingots for a new ninja to help deidara don't go for ronin or 6 path. You could go for kakuzu breakthrough, but at then you might as well just stack kakuzu instead of deidara, 6path is good, but you wouldn't run him with edo deidara. Don't go for ronin unless you plan to whale for him, he's too expensive to be worth considering and almost always he wont help you win a fight that you wouldn't have already won without him.

If you really want to spend your f2p coupons a new ninja, Madara 5kg isn't as important now. Poison tai wont help against 6path or kushina, and kakuzu can heal it off. I'd go for edo itachi and run the above mentioned team but with edo itachi pos 2, jinpachi pos 4, and earth main instead of water main.