I'm looking for the smallest router possible to use in my home network, the router must be small because it will be placed inside my ATI closet.
My current ISP bandwidth is 400/100 and i'm only going to do routing, nat and switching(vlans), no qos.
Currently i have a Archer C7 with hardware offload that is able to handle the wan load but it doesn't fit inside my ATI closet.
I've done some searches and the best option seems to be the Edgerouter ER-X, another option would be the Mikrotik hEX S( 760iGS) but it seems it's still a wip and doesnt have nat hardware offload.
Hardware wise, the GL.Inet GL-MV1000 "Brume" would probably fit the use case, but it currently isn't supported by OpenWrt (so you'd have to do the porting yourself). A supported (and better-) alternative could be the Solid-Run ClearFog Base A1 (SRM6828S00D01GE008B02CE).
Edit: as long as you don't need much more than 400 MBit/s, the FriendlyElec NanoPi R2S could be a cheap and very small alternative as well.
No, I don't have personal experiences with either of the listed devices - but was extrapolating from the information about the used SOCs in there (mvebu can deal with 1 GBit/s WAN speed, the nanopi r2s apparently with around 500 MBit/s - but it's much cheaper). Given that both options raised by the OP didn't have wireless capabilities, I omitted that necessity from the feature set.
gl-inet have their own gui on top of openwrt, which i do not use at all
from that gui, there is a link they call advanced that takes to the standard openwrt luci web interface.
and of course, i just ssh in the the openwrt command line.
imho, i would use the gl-inet support firmware and get great tech support from their forum.
they have a bunch of openwrt experts and very friendly.
Well they are a boring and cheap solution for your use case: Linksys EA4500 , $20. I've purchased several, none run hot. If you have a space consideration, take it out of the case, cut the antennae off & mount safely on bushings in your lan box. I've done this. Until openwrt 20 or 21 come along you could use the Linksys ea3500, smaller form factor, runs cool, $10, but only 64mb memory. Both are hardware overclockable for increased throughput, and reduced latency. EA6350v3 if you want unnecessary but increased horsepower, hard to find good one on ebay $40.