I don't know if it's "advice", but some things to think about -
First up would be the specs of your computer. I'm running a MBP with Snow Leopard and Windows 7, but only 2GB RAM.
Because of this, running Outlook in a Win7 VM is hit and miss. Sometimes it works fine, others it just bogs and locks up forcing me to restart the program. Btw, this is Outlook 2010 beta. I think if I had the ability to add more RAM this would help fix that problem.
Second, you will lose some of the features with Entourage. I'm using the Entourage 2014 pre-release and find it almost unusable, especially when I still have Outlook to compare. Mail setup was (for me) more difficult, but once you get that set it's done. There's no To-Do bar for tasks, so you still have to switch back and forth between screens to see everything. On the plus side, using Entourage means it's native so less of resource hog, and no VM to deal with.
Third, transferring isn't really a problem. I found it very easy to replicate all of my Outlook info in both Entourage and Mail/Address book. Almost all of my email addresses are IMAP (Hotmail & Live accts are still in Outlook only) so everything replicated just fine, and I just emailed my Contacts as vCards from Outlook to myself, and opened them in Entourage and Mail and they asked if I wanted to save them.
The biggest factor for me is the view, and tasks - I like being able to see email, tasks, appts and a calendar on one screen. Using the Mac side means using a separate program for each one of those.
Hope this helps.