I'd like to create three or four virtual machines on my Windows Server 2008 R2 OS (single server farm for now), and I'm wondering how much RAM to allocate to each virtual if the host has a total of 16GB (two 1TB hard drives) with plans to move to 32GB in the near future. I'd like to run SQL Server 2008 Enterprise, Exchange Server 2010, SharePoint Enterprise 2010, and Lync (probably run Exchange on its own virtual and Enterprise on its own virtual with SQL on the host). I'd also like to run SharePoint Server Standard and SharePoint Foundation (obviously all separate from Enterprise) for testing purposes, and I'm also wondering if the same SQL server and Exchange server can be shared by all three instances of SharePoint?
Thanks for any advice.