Exchange 2003 upgrade to 2010

I guess I'm doing the opposite of an in-place upgrade (which I see is not possible from 2003 -> 2010 regardless) so my only option is to install exchange 2010 in an existing exchange 2003 organization on different hardware which is good thing in my case.   I will be installing all roles on one server. The 2k3 environment is only one server (about 100 users). I've never done this before and I'm wondering if I'll need 3rd party software to move the resources from server to server or if anyone recommends a software to make it easier.  I've used CodeTwo Exchange migration to move from one 2010 to another 2010 but that is it.  If not will the 2k3 servers show up in the 2010 EMC and can I migrate mailboxes into the 2010 databases as if I was moving users between mailbox databases in 2010?

I'm reading that when I install Exchange 2010 it will see the existing environment and go into what is called coexistence mode.  I assume this is all automatic with install and with this it creates the security groups needed to grant the permission to allow the 2k3 servers to send to the new 2010. Also, a two-way routing group between the two

The only resource I'm using right now is this TechNet article -

Also, I'm curious if I need to get and outage window for any of the steps along the way. Is any downtime required throughout the upgrade process.  Thank you!!!
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I think you should take a look at these guides, they will make your life a lot easier:

Removing the legacy exchange server:
AmitIT ArchitectCommented:
There are several articles you can find about Exchange 2003 transition to 2010. However, whether it is a small or big setup, proper planning is required. Planning starts from Both server and client end. Also, if you current AD domain is 2003, you can plan to upgrade that first. So go like this.

1) Upgrade your current domain 2008. Not mandatory, however recommended.
2) Upgrade Client OS and Office. Minimum Win 7 with Office 2010. So user can enjoy maximum feature.
3) Finally, Exchange 2010 upgrade. In this there are several steps, so you need to write down everything, like OWA cutover, Active sync cut over, If you are using IMAP or Pop3 you need to plan that as well.

Also remember, Certificate plays very important role in 2010. This is one area, max admin fails to focus.

I suggest you to setup everything in a lab first, test everything and then plan for production upgrades, unplanned upgrades are always complex and lead to unnecessary outages. With proper planning, outage will be almost zero.

I recommend you to use MS Deployment assistant.

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