SSH limits

Hi,


I have some questions about ssh server and Linux, hope someone can help me :)

1.       Does Ssh server have a limit for the number of users that can connect ?

2.       Does Ssh have restrictions about an username length? Or
username format? We would like to use something like: foo_<GUID>

ex: foo_ 5CEB80CF-150F-4ff0-8743-A6493FA200C1

3.       Does Linux have a limit of user accounts?

4.       Does Linux have restrictions about an username length? Or
username format? We would like to use something like: foo_<GUID>

ex: foo_ 5CEB80CF-150F-4ff0-8743-A6493FA200C1


Thank you,
Adriana