domain hosting and email move to new servers

Hello,
mydomain.com now points to :
hosting at one server
email another server
two diffrent companies

i'm trying to move mail, hosting and domain to new domain name registrar and hosting.

I have duplicated the emails (to get email from both servers during propogation) and site on my new server which provides hosting and email together

now it would be easy to go into my domain name registrar to change the ip addresses... BUT, i am chaning the domain name registrar as well....

when i transfer the domain name to my new domain registrar i will ask it to point to my new server for mail and hosting.

My question is.... is this the best way to do this OR is there another way.... and does anyone know how long the downtime is?????


thank you