In my opinion you are the perfect candidate for a Hardware Wallet. You have the choice between Ledger Nano S, Trezor or Keepkey. You just invested the equivalent of $4500 - why not put an additional $100 tops and buy the best storage you can get. With a hardware wallet, your private keys will never see the light of day, and they will be in your pocket - not controlled by a website. For more than 1 bitcoin equivalent, I don't recommend any of the Online wallets, including Coinbase, any Exchange, or any PC based wallets where the keys are kept on a hard disk (or USB disk).
With Trezor (and alike), you can use their portal, or use Electrum for faster transactions, if need be. Even if you use those kind of wallets, you are still in full control of your private keys. Furthermore, if you have a combination of Bitcoin, Litecoin, or Ethereum, they can all be stored on the same device - protected by the same 24 words. Those 24 words (seed) is what you have to protect on your life, not the device itself. If you loose the device, your 24 words can replicate all your private keys (coins) on another device, or by any HD-capable wallet.