If I already have a website but later want to do the all in one website product, would that mean I'll have to abandon my first website name and create a new website name?

Assuming what is meant here is the URL or web address (aka: Domain Name) then the answer is a “it depends”. If you personally own that domain name, then you may be able to transfer it to your new website. However, if your existing website is hosted by another company and they obtained the domain name on your behalf, and own it, they may not allow transferring ownership of that domain name to you for your new website. Before signing up for any online website service and having them procure a domain name for you, you should ask how they handle transferring that domain name if and when you may wish to move website providers.