Multisite setup

Hello!

I have the following scenario, and I would appreciate if you will give me 5 minutes of your time to open the links and see what I want to achieve:

I will use the theme Native (themeforest) to build my custom website in a WordPress multisite install using sub-domains. Later, I will purchase different domains for each of the website and use the domain mapping plugin.

As I read in the rules, I’m not allowed to post excessive links so I will only write where to find the products I will use. On the marketplace that begins with “EN” and ends with “VATO”.
Please check:
Native
WPLMS
WPLMS APP
Bimber
Newspaper
ListingPro
ReHUB
InJob
I want to achieve this:

Install Native on the main website ( site.com ). As I told you, it will be a wordpress multisite install using sub-domains.

So the websites (as I planned) will be: domain/subdomain — Theme
Site.com — Native
account.site.com — Native
1.site.com — Native
2.site.com — Native
3.site.com — Native
4.site.com — WPLMS
5.site.com — Bimber
6.site.com — Newspaper
7.site.com — ListingPro
8.site.com — ReHUB
9.site.com — InJob

I need my users to be able to register an account (so I planned account.site.com to redirect all the login / register buttons from all the website to account.site.com ).
They register only once and then they will be able to login on any of the websites. They click login > redirect to account.site.com > after they login, they will see buttons to all the websites within the network. When they navigate to any of the websites from the network (multisite) they need to already be logged in.

Issues:
#1. As you can see some of the services within this eco-system have different roles (eg: WPLMS, the e-learning platform have roles like instructor and student each with different dashboards. ReHUB have buyer and seller.) I need to have a custom field to the register page where the user will select the role he wishes to have.

I’m opened to any alternative (if you have one for me). I don’t think it’s the best setup I could do, but it’s the best I could think of.
I see that there are plugins that sync cookie and sessions so the user, once logged in, it will be logged in on any website form the network that he visits.

I run a non-profit organization and the project is philanthropic so I don’t have a big budget to invest in custom solutions, so I need to get the job done with what I have (what I can afford).

Any additional information / help / links will be very much appreciated!
I’m willing to post any credits to you or your website / products.

Thank you!