First of all it's not a good time to buy Bitcoins at a higher rate ($400) but it's alright since you've already bought it. 
So my question is: Once i buy my first bitcoin, what exactly do i do with it? Do i leave it in my coinbase account? Is it safe there? Or do i transfer it to my desktop computer?
Well, as of now you can pretty much leave it there or if you are paranoid enough, then you may store it in Coinbase's vault which is much safer than your primary wallet due to activation of several authentications. (Email, 2FA etc.)
I plan to always keep a balance of 1 bitcoin in my account for 5 years to 10 years,
Then I would advice you to buy a Ledger Wallet which is the most secure way to hold Bitcoins. You can have a look into their setup videos in order to know more about it and how secure it is.
And if you really want to store it somewhere safe and don't want to touch it, then you may buy one of these physical coins, print out a private key from your offline computer and preserve it under the coin with a tamper-evident hologram sticker. You can contact Mitchełł and buy one of these coins from him.
Hope this helps you out.
So my question is: Once i buy my first bitcoin, what exactly do i do with it? Do i leave it in my coinbase account? Is it safe there? Or do i transfer it to my desktop computer?
Well, as of now you can pretty much leave it there or if you are paranoid enough, then you may store it in Coinbase's vault which is much safer than your primary wallet due to activation of several authentications. (Email, 2FA etc.)
I plan to always keep a balance of 1 bitcoin in my account for 5 years to 10 years,
Then I would advice you to buy a Ledger Wallet which is the most secure way to hold Bitcoins. You can have a look into their setup videos in order to know more about it and how secure it is.
And if you really want to store it somewhere safe and don't want to touch it, then you may buy one of these physical coins, print out a private key from your offline computer and preserve it under the coin with a tamper-evident hologram sticker. You can contact Mitchełł and buy one of these coins from him.
Hope this helps you out.