Ondine, an i3 definitely will not be sufficient for full orchestra. The specs for full VSL use - with MIR Pro - would be at least an i7. Real world performance will vary from individual to individual based on workflow, but for most, an i7 4930k or the older 3930k i7 will be more than sufficient. Dietz has remarked that in the case of his own specific workflow (and this is a specific example - not a general one), on his i7 3930k he is able to get around 100 VSL instrument tracks in MIR Pro.
Using SSDs, with their reduced required loading buffer for VSL samples, 32 gigs of RAM will likely be enough. If you use a lot of sample libraries by other developers, there may still be a potential need for 64 gigs, but I cannot directly speak to that, as for what I write and do, I more or less live in VSL land. What I can say is that in my existing system (an i7 930 with 24 gigs of RAM), is that more than 24 gigs would be helpful. Note also that I currently have only one small SSD drive so not that many of the loading buffers can be reduced.
Also, the VSL developers have stated several times their libraries perform better on the Windows platform than on Mac. The DAW builder I am most familiar with also confirms better overall DAW performance on Windows over Mac, and for quite awhile that company (ADK) tested and sold both PCs and Macs. Windows certainly can handle RAID, but unless you intend to be very high-end, streaming from SSD's without RAID is enough.