can you tell me that the seals minato used were all the seals he learned from kushina? No, you can not. Plus there is his affinity. He was trying to take the rasengan to whole different level by doing what kakashi and yamato told naruto to do. This means that minato had his own affinity. Just in this, I have shown you that we don't know the full extent of minato's power yet because we don't know enough about him.No, we have seen the extent of his power. We've seen Minato in action using his Flying Thunder God technique, the Summoning Technique, the Rasengan (against Madara, for example), a space-time barrier technique, a Contract Seal, and we've seen use various sealing techniques. Such was the extent of Minato's powers up until his death. If Minato were to live longer, he would have gone very far, but that in itself is an assumption - we cannot know for sure.
But one thing I don't agree with is your statement about the Moon's Eye Plan. You mean to tell me, that Madara, who has been said to "know everything," according to the Fifth Mizukage, is working towards a goal that has been a failure from the start? That seems extremely unlikely to me. Madara has an incredibly vast knowledge of his world - why wouldn't he know that Minato divided the fox's chakra into two, one part having sealed into Naruto, and the other with himself? You can't just write Madara off by saying "he doesn't know;" if he didn't, then the series is not that interesting anymore. That means all the manga readers, according to your logic, now know that Madara's plan will not suceed. What are we expecting then? It seems more than likely that Madara does know, and perhaps in a flashback of sort it will be revealed exactly how he has figured it out.
Just because the fifth hokage said that masked man/tobi/madara knows everything doesnt mean that madara saw what minato did that night. You can't show me madara witnessing what minato did when he sealed half of the nine tail demon fox into naruto. You can only assume to your own advantage that he knows what minato did that night. Plus minato is linked with his seal marks in some way because he can choose which seal he wants to appear on and how. Madara was tagged with this seal mark so I don't think minato would be careless as to explain to kushina what he was going to do out in the field and do the process while madara was still there. He would have known that madara would be there. This is why naruto is going to be very long.