20k would take about 20 weeks if you max out convoy/plunder and the group wheel. As well as staying on 1 hour for the 10 coupons. As for what ninja will appear? Probably something that would be a good position 2 support or a previously god tier ninja that has been a bit power crept. Its mainly on the other events that appear. For instance, last time there was Six Paths Naruto in lucky stars with Fuku deals being the new Gamariki summon and Konan Taisho. When I did fuku deals, it was Konan Angel of God in Lucky Stars with Edo Roshi in Fuku deals.