•Is the SQL Server Management same as Standard edition?
Yes
•Does it allow hundreds or thousand of users to make to connection to
it?
If you give it enough ram and program stupid enough that t his is needed, yes. Normally it is not needed - a connection shoudl be reused and only be open during processing, and there is no way you process thousands of pages at the same time. If you open connections ad paage start, close them at th end you will use only very few connections for thousands of users.
That said, performance may be an issue. Make sure you buy HARDWARE suiteable for your load.
And your client should consider RENTING using SPLA. A lot cheaper, monthly scalable and never pay for updates.