Since the Azure Stack Architecture blog became rather long, this blog will cover the second part. You can find part one here.

Initial Azure Stack VM sizes

In Azure Stack TP2 there are only a handful VM sizes, but at GA a lot more VM sizes will be supported, although not all VM sizes can be accommodated yet because they require specific hardware configuration. Continu reading here 

Source: Dive into Microsoft Azure Stack Architecture (part 2) | Azure Stack