do you really advise windows users to move to linux environment ?
That's not what I said. I said:
I expect the vast majority of experience and expertise out there running large sites is going to be on Linux.
That's a very different statement. If I were going to build a new large-scale system, I wouldn't consider using anything but Linux. Moodle is much more heavily tested and used for big systems on Linux than it is on Windows. I've been running Linux systems for 15 years, though, so that's a much easier decision for me. Because you don't have any Linux experience, that makes the decision much more difficult. If I were you, I'd be *very* cautious about building a large system on a platform I don't know - too many opportunities for project-killing rookie mistakes.
I'd recommend two things:
1) Stick with what you know until you have a compelling reason to make a change. Test it on Windows first. Load test it. Push it hard and see if it will hold up under your expected traffic load. If it doesn't handle the load, *then*:
2) Get some help. Hire a consultant. There are many good Moodle partners
out there who *do* have the requisite Linux expertise. Hire them to help and teach you what you need to know.
Visvanath's suggestions are good ones. Grab an old desktop and fire up a test system on Ubuntu Server. Play with it, get a feel for it. fire up a LAMP stack on it and load Moodle on there. Learn to love the command line, shell scripting, and all the tools that come with Linux. Get comfortable with Linux in a non-production test environment where it's OK if things go wrong before ever considering to use it in production.