Not a fan of most Norton products myself, but do know many that use them and like the overall experience. Depending on your online habits it might be beneficial to use a VPN. Also depends on your purposes and needs. What else are you using alongside Norton? Never ever put blind faith in one AVAM solution. Windows Defender has gotten better, MBAM Free and Premium are decent offerings, but there are plenty of other options. I suggest MBAM Free and running regular manual scans. There are many cases still where one AVAM solution will detect something another one misses.
For gaming, no. VPN's encrypt traffic, this creates and requires overhead to accomplish. You also want to take advantage of higher levels of encryption where you can. This can cause bandwidth and processing losses, but the point isn't speed it is protection. Pick one, you can't have the other. If you water down the encryption on a VPN to have speed, it almost negates the purpose of having a VPN in the first place.
Shopping and banking sites you use should be operating with encryption in-place under HTTPS. While that isn't fool-proof or highly protected, adding an encrypted VPN connection between you and them wouldn't be a bad idea. This also depends on the VPN service you decide to go with and how they monitor and report the traffic from the VPN tunnel service you pay them for.
In best-case scenarios you'd want a site-to-site VPN, meaning your site is directly connected via VPN to another site, in many cases this is what organizations and businesses do to connect different regions securely. This however isn't helpful for many end users looking for a more generalized and open service.
Essentially you'll want to make sure you go with a VPN service that is able to maintain a level of bandwidth that works for you, and is able to maintain appropriate levels of encryption, DNS leak protection, and check their guidelines for record keeping and reporting. For some folks that last one is a big issue, but that ethical debate isn't for here and now.
Smart browsing practices, maintaining responsible access control (how and where you choose to save credentials, use the same or different credentials, password complexity, what device(s) you access specific resources on) can make a huge difference on your level of security risk. A VPN isn't a sure-fire safety net, sloppy habits will still cause negative results. Not saying you have those qualities or are that way, but many folks expect a VPN to be more than it is....which is an encrypted connection between one device and another device over a network, for the most common example: PC/Router to Server/Router over the WAN (Internet).