scorz wroteI am not that much of a hardware guy.. but why Haswell? Go for skylake it's only 3$ more and it's a recent technology. As for mobo this sound ok: MSI B150 PC MATE (DDR4) USB 3.1 (LGA1151) (99$)
And I suggest an PCI-E ethernet.
PS: An external ethernet won't slow the CPU in a remarkable way. But you're building a server not gaming/regular PC so it's like playing on the safe side. Plus since you're not installing a GPU, the CPU will handle some minor graphics stuff.
PS#2: I think 16GB RAM is overkill, but after all it depends on how much users will be connected so..
PS#3: If you can find a used/new Xeon CPUs + mobos (LGA 2011/LGA 2011-v3) within the budget, go for it they are much better for servers
you are right about the skylake , i was looking for a cheaper option .
there will be no graphics whatsoever , just the main setup .
the 16 GB ram was asked for by the application implementor ( i told him it is too much for a pc with only IIS on it , but rams are the cheapest these days )