Before I answer the question(s), let me remind you that selling accounts is against the Terms of Use (ToS) of both Sony and Nintendo:
Sony:
COMMUNITY CODE OF CONDUCT
[...]
- You may not sell, buy, trade, or transfer your Online ID, Account or any personal access to PSN Services through any means or method, including by use of web sites.
Nintendo:
4. Limited License.
A. Nintendo. Nintendo grants you a limited, non-sublicensable license to access and use the Services for your personal use only. Such license is subject to these Terms and does not include: (a) any resale or commercial use of the Services or the Materials therein; (b) the distribution, public performance or public display of any Materials; [...]
As for the questions:
- Can I use multiple accounts on 1 Nintendo Switch and play all their games?
Yes, you can. However, a single Switch can only hold up to 8 accounts at any one time.
Also keep in mind that the Switch handles accounts a bit differently from the PS4:
On the PS4, you will be automatically signed in to the last account you used. To use a different account, you must switch to it.
On the Switch, there is no default account. Every time you want to launch a game or an app (including the eShop), you must choose an account. This feature can be disabled, but only if there is only 1 account on your Switch.
- Do I need to do similar 'tricks' like on the PS4? Or does it work different there? How?
The Switch uses the same "Primary Console" mechanism the PS4 does. This means:
- Each account can only have 1 "Primary Switch" registered.
- There is no limit to how many accounts can have the same Switch registered as "Primary".
- If an account has downloaded content on its "Primary Switch", any other account on that Switch can access it.
- If an account has downloaded content on a Switch that is not registered as "Primary", no other account can access it.
Thus, sharing games works the same way on the Switch as it does on the PS4.
- Is there any other restriction/hurdle which makes this PS4-way of separate game-accounts impractical/impossible?
As mentioned earlier: you can only have up to 8 accounts on a single Switch. If you wish to create another one, you must remove an older account first. This also applies if you attempt to transfer an account to a Switch that already has 8 accounts.