Help with Migration to SBS 2011 from Server 2003 Enterprise without removing the old server

I'm working on a phased migration from a single Server 2003 Enterprise Edition system running SQL Server 2000 to a 2-server setup using SBS 2011 w/ the Premium Add-On. I started my research by making sure a 2-step approach to the migration could be done, and I've outline what we're doing there:
https://www.experts-exchange.com/questions/26965973/Help-with-phased-migration-to-SBS-2011-Premium-from-Server-2003-Enterprise-with-SQL-2000.html

In addition to whether this approach would work (which we've established it should), I've got a couple questions relating to the how - all of the information on migration installs that I can find is for migration from SBS 2003.

Here are our questions:
1) Which, if any, of the pre-migration steps outlined for migration from SBS 2003 will need to be performed for the migration from Server 2003?

2) Will we have any troubles leaving the shared folders on the source server?

3) Will the process of installing SBS 2011 on the new server disrupt the source server? My primary concern is whether we can do the setup during the business day, which will require that shared folder access and SQL Server stays operational while the install is running on the new server.

4) When it comes time to setup the Premium Add-on on what is now the existing server, is there any way to do so as some sort of migration or even in-place upgrade, or will it be a completely manual process clean install?

Thanks in advance!