Do i need so many different wallets, or is it enough to have just one?
One is sufficient. I'd recommend 2-3 wallets if you're holding significant sums but I doubt that you do given your knowledge.
The next question, do i pay fees to transfer from and to my wallets?
Yes. You need to stop thinking of the old definition of a 'wallet'. In Bitcoin it is just a collection of keypairs that makes it easy to use Bitcoin and interact with your addresses. When transferring the *between Bitcoin wallets*, there is no concept of ownership, so whether you're transferring from your address to your own again, or from your address to someone elses, doesn't matter. You need to pay fees.
Thanks for a proper answer. That means i have to diversify my coins on a a few wallets for storage if i invest a large amount of money into cryptocurrency. At the moment i have such a low investment, that it is not profitable to swap all my coins into my wallet. Would u suggest to swap only my longterm coins into the wallet? Some exchanges are going crazy now( a friend told me), should i save them all now?