Migrate a website to WordPress, Upgrade to HL7 report uploads

Basic Summery of the task
We currently run a website in an older version of PHP, www.youth-revisited.co.uk
we would like to transfer it to WordPress and make some upgrades to it. Most of the site will look the same it just needs moving over to a different system. If we can move current customer data that would be great.
Front end and back end are both important, HL7 Reporting will be a new feature. Knowledge on this is essential for the job. Plus updated Practitioner use.

Front Of the site:
Products
All the products and pages can look the same as the current site The information will also be the same.
Payments
We use Stripe as our Payment gateway. Some customers will also have credit facility which we will need to work a system for.
New information
There are a couple of pages to add, and some amendments to make sure it is all mobile friendly and smooth to run.
Redundant information
Originally the site was an online pharmacy, it is not a pharmacy anymore so there are things from the site that we no longer need, making it simpler to use and more streamlined

Upgrades
Currently we supply directly to the customer
We would also like to have options for Practitioners to have their own logins to create orders for their customers and an affiliates section for people who have clients that pay directly, and we offer them commission for those orders
Ref: https://www.forthwithlife.co.uk/partner-with-us/
We would also like to link a what App so we can send notifications on mobiles as well as email.
And let people place orders for other people.

Back End Control Panel
We can currently manage the daily orders customers, practitioners, phlebotomists, products, pages and reports from a control panel. This back area is important. As well as a payment receipt we also need to create a Lab form for orders placed this has a qr code with specific date required by the labs to produce reports.
We would like to upgrade our back end to include a HL7 system where a report created by our labs us uploaded to the customer’s account automatically https://app.forthwithlife.co.uk/ (another reference site)
We have been running for 4 years so any metatags, and seo ect we would like to have moved over so it doesn’t star us as a brand new site.

There are a few companies with similar sites that provide the same service as us.
https://medichecks.com/
https://www.forthwithlife.co.uk/
https://www.letsgetchecked.co.uk/

to help you get an idea of how it works.