Q:

1. I want 50 mail ID for my domain ( mail@mydomain.com) but my domain registrar only provide 2 mail ID per domain. what will I do?
2. I want a personal wiki site that can see and edit only by my colleagues.
3. I want a document editor which includes pdf, xls doc etc. Also want to save all it one place.
4. I want to make presentations and share it with public or only with friends.

A:
        YES!
now you can do all these things by setting google apps for your domain.
You can start by now by clicking here.
Here is a help page from Google. If any doubt, just drop me a mail.