New Budget VM Server hardware suggestions

Hello I’m currently thinking about building a new VM server and would really appreciate it if you could help give suggestions on hardware.

The new server will be used to replace a couple of gaming PC’s, a router/firewall (pfsense box) and possible a storage server (Thinking about freenas but looking for a lightweight alternative)

Host: Likely Debian 9 since I already have working experience with it or maybe XCP-ng
VM 0: pfsense box/firewall (1-2 cores)
VM 1: Windows VM with GPU passthrough (~4 cores)
VM 2: FreeNAS or similar with a LSI PCI card passed through (~2 cores)
VM 3: Likely some version of Linux for testing stuff with another GPU passthrough (1-2 cores)

For the GPU’s we will probably be using a R9 570 + GTX 1060 or some R9 380’s since we already have that hardware.

These are the spec’s that I’m thinking about using:
Ryzen 7 1700 or 1700x
R9 570 + GTX 1060
16GB or more RAM
a couple of SSD’s directly passed through to libvirt for OS drives.
Hard drives currently unsure at the moment but most of them will be passed through to the FreeNAS VM.

TDLR: I’m looking for a fast, cheap CPU + motherboard ideally with as manly 16x slots and RAM slots/capacity available also ideally something that doesn’t use allot of power.

What is the budget?

Ideally under £400-£500 since I already have everything expect a cpu, motherboard and some extra ram also thinking about getting a new case with a bunch of hotswap bay’s so the budget is closer to £300-£400