make a template of a page which my client will only have to choose which content

Hello everybody.
I’m building my first site using wordpress. so far it’s been a challenge but managed through it. Although there is a problem I don’t know how to solve.

My client has 8 products which he sells (not ecommerce store but frontal sales) and he wants a section in his site in which his clients could put username and password and log in and view their purchases.

My client, after every sale he makes, will go into the dashboard and subscribe a new user. That’s easy. My problem is that I want my client to be able to attach a page suitable for that particular client.

What I thought about doing is making a page template- a header which is static and won’t change between the users, and below it 8 places to show content.
For each user, my client will choose the content inside his page.
For example out of 8 products, one of my clients client bought 3. So I want my client to be able to open a new page and select from a drop down list or a select list the 3 items suitable for this particular user.
Every product has 10 articles attached to it.

Is there a way I can store all the information for 8 products + their articles and my client, on opening a new page, will only need to choose the products suitable for that user?

actually what I’m asking is –
is there a way to customize the “add new page” section to be, instead of writing or coding the page content, suitable for a particular template in which my client will only have to choose from some sort of list, which content he wants to show out of the possible options (8 products, so 8 options)?

Thanks in advance.