Hi Sandy,
To answer your question, yes, for the most part you can just install new servers. It's actually pretty straight forward. I wouldn't think order matters too much from a system perspective.
Server1: Its very easy to complete this one. Just install another Management server and instead of creating a new DB during the install, just point to the existing one. The only additional caveat is that you will need to make this new one
the Workflow server, the primary management server. This is outlined in the Disaster Recovery steps found below.
http://technet.microsoft.com/en-us/library/hh495516.aspx
Server2: This is the only one I've never completed. I am thinking you could unregister the old DW Management server, keep the DB and register a new one. You might want to test that one out if you can. The DR steps outlined in the
above link mention you can just install a new one, so it should work.
Server3: This one is the easiest. You can just install another portal server with no impact to the system. Point users to the new one and turn the old one off.
I hope this helps.
- Christopher