I can't help you with components that have a good track record with Adobe Premier as I don't use the program and don't know much about what does and doesn't play well with it. What I can recommend if he wants stability over bleeding edge is to look for the "Corporate Stable" boards. I know Asus makes them and here are two currently on Newegg with an Intel 1150 socket.
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www.newegg.com/Product/P ··· 13131988»
www.newegg.com/Product/P ··· 13131990They are Q87 and H87 boards respectively which are one generation behind currently. The H87 is simply a stripped down Z87 that lacks the ability to do SLI/Crossfire and overclocking (both things you are unlikely to need or want). The Q87 is the top of the line "business" grade chipset and has similar limitations of H87 but adds things like vPro (which you also likely don't need).
They both have the same additional PCIe 2.0 channels (8), the same USB ports (6x 3.0, 14x total) and the same SATA configuration (6x 6Gbps ports). They also both support 4 RAM slots with a max of 32 GB capacity (to get beyond this will require going to AMD or Intel 2011 socket).
If he really wants the ability to expand from 16 to 32 GB, you're going to need to populate with 8GB sticks unless he wants to remove sticks in the future (usually a waste). The downside to this is those sticks tend to be expensive.
Here's the full search results if you want to see the others (there's some built around the current gen chipsets, even a Z97 board). »
www.newegg.com/Product/P ··· eSize=30