Power looks alright for both cards.
Maybe someone else can comment on the board. Sticking the 2nd card into the PCIe x1 slot may degrade the mining performance.
Something to consider...
Maybe you want to expand the set-up later on.
Look for sale items, maybe you can get a decent 750W power supply later on that can supply more cards.
I would personally go for a board that has more PCIex16 slots. Then you can always add more later on and do not need to scrap your entire rig, when you get tired of it.
From previous readings in the tech help section as well as the mining rigs section, I don't believe there would be any degradation with regards to mining performance if OP decides to use 1xpcie --->16xpcie adapter. However, the power supply is KEY - don't go cheap on this one, especially with multi gpus.