use of Migration manager for AD"

1. huge complex and old (still 2003 DCs exist) environment - 25 domains should be migrated to one.
5 years ago we had discussions with Quest (at time it was under DELL)...
I remember that the product could be used only by consultant company with trained/certified by QUEST people.
Is it the same situation now or a customer can purchase the product and have full support from Quest directly?

Yes, Migration Manager is a Services Mandatory product. It is a very complex configuration, needs to be configured per each project specifically, and should it be configured incorrectly could cause damage to a production environment.

2. Does Migration Manager include tools for analyzing the current forest state prior to Migration?
I guess that there should be a tool for detailed reports for: accounts, computers, groups, servers and all other things...
Migration Manager itself does not include such tools, but one of the tasks of a services team member is to analyze the current configuration prior to any project. We also have other products that can assist with this analaxsys. A sales person or account manager could assist with this.

3. Can tests for accounts migration be performed in production without any harm?
I will appreciate some high level general explanation of how it will work.

Yes, the product can perform test migrations in the production environment without impacting any production, but it's always best to first setup the product in a production simulated lab, to understand the functionality, and possible gotchas you may encounter along the way.

4. I guess that Quest Migration manager server should be installed in one of domains in the forum and collect the info for.
Migration Manager can be installed in a stand alone capacity, even in a workgroup should that be desired, but a services person involved would be best to suggest proper placement for your particular setup.

I know a lot of this may sound like we are simply trying to sell services, but honestly these projects are large, complex, and requiresomeone knowledgeable that can assist with the implementation and success of your project. If I didn't say this, we would simply be setting you up for failure.
Luke