Myth 5:  

You must hire expensive Subject Matter Experts for your migration-False

FALSE

This is absolutely false if you have some bright folks on your team who understand Powershell and Directory updates.  Having been hired to do many of these types of projects, I can say that I am usually only involved in the first 20-30% of the moves.  So someone like me is often involved in the beginning phases to get the migrations teams quickly ramped up and the process defined and refined so it is easy to repeat.

Most organizations just don't have the time to (self) ramp up and continue to perform their day to day operations so bringing in an outside person/group to kick things off is pretty common but certainly not a requirement.

For example, unless you have done a considerable number of Cross-forest migrations, you may not truly appreciate the negative impact WAN links and remote Domain Controllers have on the process. Intra-Org moves say between two sites in the same organization works perfectly and rather fast. In a Cross-Organizational move however, the performance of the migration can be painfully slow and AD replication will offer considerable delays and even potential problems with conflicts. Moreover, targeting Exchange servers in various sites and locations means you are never really sure how fast the process will be and your projections will likely be WAY off.

Understanding those potential obstacles up front means you can plan around it and put into place a very consistent, reliable and predictable process. Here is one example of a process we have refined with experience:

One thing  we have learned with this model is we do not have to change the migration scripts to target different DCs and servers and most importantly we know exactly what our migration capacity is and can hit our projected numbers every single time with no surprises. As I mentioned before, it is also important that the target Exchange servers have only one storage group and one mail store. This will eliminate a potential problem with mailboxes that may "split" across stores.

To move people to remote servers after this move, you would just use the normal Move-Mailbox command or even the GUI to distribute the mailboxes. This process is reliable and a simple "Fire and Forget" operation since you can just queue them up before you go to bed at night!