What do you guys think is the best alternative?
Its better if you buy at Coinbase, i have been buying and using their system for 1 year now. As for Gemini and Blockchain i havent tested buying and verifying may account there.
I,m going to buy to an offline wallet?
Youll definitely need Ledger nano S. The most secured offline wallet that you will ever need to store your coins.
And is there a fee for sending my bitcoins between any of those places and my offline bitcoin wallet?
Every transaction goes though the network and you will be needing to pay fees to transfer from your web wallet to your offline wallet.