Migrating WPMU to a new server...

I am new to MU but I usually setup new mockup sites on my server then when ready move to the clients domain. Its easy to do in a Wordpress single site without cloning tools or plugins.

What do I need to look out for if I do the same with WPMU and want to move to a new domain & server?

It seems a lot of people have problems and I am spending a lot of time trying to get plugin created that creates subsites via a reg form and want to be sure that works and an my blog template plugin.

I know there is an article here:
but that is like 6 years so figure it may not still apply? If not is there and updated version?

Or I found this?