How much a VPN will slow you down depends on the hosting company, which of their servers scattered around the country and around the world you are hitting, time of day, network load, server load, in other words typical network speed considerations but there is/are added links in the chain.
Laboriousness depends on the particular VPN provider and the design of their client on your MacOS or iOS device. Again depending on the VPN provider there are a number of different payment options. VPN Unlimited even offers a three week "vacation" option.
HTTPS (Hyper Text Transfer Protocol Secure) which you will see in the URL and confirmed by your "green padlock" does provide for encrypting traffic both directions. But as I said previously
Whatever security measures can be created by humans can be subverted by humans.
and a sufficiently determined thief can break that encryption. Using VPN would not replace HTTPS but would add another layer of security and encryption.
Back in the heyday of mainframe computers, it was thought the volume and complexity of their data was sufficient protection. That evolved to a security philosophy that you were secure if it would cost more to break the security than the value of the protected information was worth. Today the use of thousands and tens of thousands of slaves (computers owned and operated by unwitting users) and
bots spawned from those slave computers constantly roaming the internet looking for any vulnerable computer, breaking security costs next to nothing. In fact
Ransomeware has emerged as a highly profitable enterprise.
