Changes may be a flat monthly fee, free as part of a larger retainer (if simple) or ad-hoc pay as you go based on amount of work.
It's not a lot and doesn't form a big part of the business but helps provide an all-in-one solution for clients who typically have no idea where to go next.
One thing we are winding down and I urge you to avoid is email support. It's simple to set up but you can quickly get overwhelmed by the amount of support involved. Email is often a fundamental to business, depending on industry, and it should be treated as such. We suggest clients use Gsuite. This leads to my final point.
You are not a hosting company, unless you pivot that way. You are not an email provider. You are a web design business and you should not let hosting overwhelm the core of what you do. Be ready to cut it off if it distracts too much from your core.