Help with usernames, PCRE-type regular expressions

[kpmedia]

Need a little help here, trying to limit usernames for new registrations.

I can see this in admincp vB options, but it's either too much filtering or not enough:

You may require the username to match a PCRE-type regular expression.
(Do not start or end the expression with an escape character)
Examples:
^[A-Z]+$ - Characters from A-Z only
^[A-Z ]+$ - Characters from A-Z including space
^[A-Z0-9 ]+$ - Alphanumeric characters including space
^((?!&#\d+;)[\x20-\x7E])+$ - ASCII characters from 32-127
See PHP.net for more information on regular expressions.

I want A-Z, 0-9, periods, underscore, spaces and hyphens --- and that's it.
Any help on what this syntax would be?


Also...

And if you know how...
Preferably no "repeat" periods/underscore/hyphen/spaces.
i.e., "--BESTUSEREVER-- ___ -- 123"
Better yet, limit to two total periods, underscores, hyphens, spaces
I don't want any more users trying to use screwball usernames full of ASCII.
Or even overusing what is allowable non-letter/non-number.

Thanks.