Can I change package or add a module later?
Yes, any time, after launch too: a presentation site can become a shop, and you ask for a module or Premium in the portal.
Where to ask
In the portal under My subscription → My package you see what your monthly fee is made of and what you can add with a monthly fee. The add button requests the item.
What involves work
Adding a module (Quote requests, Online shop) or Premium involves work, so it becomes a request. The request continues under My requests: you get a quote, accept it and sign the related annex.
What starts right away
Hosting items that need no work (for example a higher hosting tier, CDN, an own database server) start right away. The prorated fee for the current period is charged to your saved card, and the monthly fee goes up from the next charge. The confirmation window shows the amount beforehand.
One item once
The same item cannot be requested twice: while the request is running, the button shows it as already requested.
Let us look at your site.
The quote form takes two minutes: package, add-ons, your company details. You see the price at once, and it commits you to nothing.