Help with Gen

Nitmitz is a good substitute for the navy gens you want to buy with his flexibility as navy-air gen & his discount. Despite a skill slot wasted on Cmpuflage, you can still configure him to be a good navy gen.

Yamamoto is good if you want a arty-sea hybrid. As he has max potential 4* in arty allowing him to deal above average dmg when taking about gens. His 5* in navy allows him to be used as a non-carrier navy gen if you don't have a navy gen yet. Yamamoto's skills & 6* in air, however, makes him more of a air gen. Depending on your use of his air skills, he may be of good use to you. Wolfpack is useful for Invasions,

Donitz has potential to be absolute master of the seas, his movement also allow the slower navy types he command to move as fast as, if not faster than subs or destroyers. Of you want a pure navy gen to rule to the seas, Donitz is your guy.

But Konev is art,and i dont have good navy. And a lot missions needs navy. Or i m wrong?
Or better to do not buy anything and spend all medals on upgrading my gens?

Your Eisenhower is a good navy-air hybrid, isn’t it? He may not be the top navy gen, but you should be able to do a lot of invasions with him. To occupy the top spot of your navy general list I would recommend Nimitz ou Yamamoto. If you get Nimitz with -40% it’s a bargain.