Well.... our DCs are around 25-40GB depending on the age and number of Windows patches. Such a small VM will easily fit on any of the SSDs today so go for 2xSSD in RAID1 because the slowest SSD will out perform the fastest spinning drive(we leave sequential reading with huge blocksizes out of the game) so your Terminal Server VM will benefit.
We dont like that a Fileserver becomes part of a DC. How much space you need for the File Server? If is will fit on the SSDs... go for SSD.