I agree, if you have to ask, then you should start by answering those questions by doing research yourself instead of asking others on a message board.
I can tell you that Google has a few thousand servers running their search engine.

I can't remember the exact number.
As for Instant Messaging, there are a few open source ones out there like Jabba which are easy to install and customize - but plenty of people have done that already.
The competition in search engines are stiff - even big players have tried it and gone.
The same goes for webmail - to distinguish themselves people are offering large amounts of hard drive space.
If you want to just "play around", you can start your own search engine, webmail and IM within 2 hours.

But if you want to be serious, we are talking 90% advertising and promotion - marketing is key, and you need money to advertise. Start small first - never over-invest in hardware you don't need - many companies have gone bankrupt by spending half a million bucks on hardware to realize they are not getting the visitors that require it. So start small, always have hardware that is
just enough, and advertise heaps.
