When there is a wire between the two interfaces, the limits are the hardware and drivers of those interfaces, and the "physics" of the Ethernet medium and the protocols for Ethernet.
When you have a switch in there, you add two more interfaces, as well as the logic to determine which port (or ports) to send the packet back out on. A key metric for enterprise-grade switches are "packets per second" rather than bandwidth. Since there is a cost for each packet, how many per second can be handled is much more important, especially as in real-world situations many/most packets don't carry the "full" payload (typically 1500 bytes).
A used C7 at a cheap price is a decent choice. If I were buying a new router, I'd agree with the advice given by @slh and go with a current, multi-core device with plenty of RAM and flash if your total budget is under US$200. While I have no experience with them past looking at the specs, as an example, the ASUS RT-ACRH13 is US$63 on Amazon, compared to US$65 for a new Archer C7.
If I understand your ascii art, then yes. Basically wire all your desktops and servers into the cheap gigabit switch, put an uplink from the gig switch to your router, and you're done. All the LAN traffic will go through the cheap gig switch, only traffic between wireless and LAN, and between LAN and WAN will go through the router.
For double-plus value, use an AP instead of a standalone router and plug the AP into the switch as well (TP-link eap 225 v3? use stock firmware). If you go this route you might prefer a managed switch, like the TP-link TL-SG108E or Zyxel GS1900-24E or like jeff said a used Cisco.
At the router location, that espressobin looks good for 100mbps or even 200 or 300 mbps WAN, with the powerful ARM chip it should NAT and shape those speeds.
Honestly if you're looking to NAT 1 Gbps (940 Mbit?) I would spend the extra money and get an R7000 or R7800, something that is known to handle a ton of NAT bandwidth. Keep in mind though they wouldn't be able to do QoS/shaping at that speed, maybe half that. You'll need to be using FastPath/SFE to hit 1 Gbps.
ipq40xx is the name of the OpenWrt target, covering the Qualcomm-Atheros ipq4018, ipq4019, ipq4028 and ipq4029 SOCs, the wiki is a bit sparse on this SOC so far, but you'll find a 'list' of the supported devices here https://downloads.lede-project.org/snapshots/targets/ipq40xx/generic/.
The WAN here is only 100mbps, from the original post:
The issue seems to be confusion between the term NAT and the term LAN. NAT is the process of translating packets as they go from WAN to LAN or back, the OP originally states that he has no concerns about this speed really.
The concern here seems to be to keep LAN to LAN communications high, esp wired but maybe also wireless. Some benchmark showed the C7 "only" hitting 950 Mbps, but the truth is that on gigE there can be all kinds of reasons why you might lose that 5% of the speed, including things that have nothing to do with the C7. In any case, a gigE dumb or smart switch between your high-speed wired devices will take care of any concerns. Then it just comes down to: what do you want your Router to do? and that's a whole different kettle of fish: tradeoffs like cost, shaping speed, QoS, additional services... those all enter and have nothing to do with the original question.
A Dlink DIR-860L B1 is a nice device if your still able to find one...
I recently bought 3 of those at ebay (eu) for a very cheap price (one was even sealed) but you have to be make sure that they are rev B1 and not A1.
Right now I'm only using them as smart switches + Wifi AP together with my WRT3200acm but i heared they do a good job when using them as real routers with SQM aso.
In my setup they are rock solid with one of the latest Lede 17.01 Snapshots and there is even a optimized community build available with some very useful preinstalled features.
Lovely devices with decent Wifi performance. I'm very happy with these little boxes...
First of all there is no tp-link Archer C7 device. There are several very similar devices that somewhat work with LEDE - namely tp-link Archer C7 v2, tp-link Archer C7 v4 - or not. With different features and different number of antennas.
If you buy just "tp-link Archer C7" you may get hardware revision v3 or v5 that DOES NOT WORK WITH LEDE.
I own Archer C7 v4 and it is supported ONLY by development branch of lede, so you have to struggle hard because there is not web GUI for you out-of-the box.
My Archer C7 v4 is a great device.
I use it with gigabit ethernet WAN connected to Huawei optical ONT terminal.
It can pump ALMOST full bandwith of 300Mbps on WAN d/l on both IPv6 and v4 - actually closer to 260Mbps, not reaching 300Mbps.
BUT
I had to learn how to configure it using command line until it is able to connect to internet, just to download webGUI...
Owning both a C7 v2 and v4, I can confirm that with fastpath offloading you will be able to get approximately 930mbps LAN-WAN. LAN-LAN is no problem as stated in previous posts. The discussion about 9x0 mbps vs 1000 is more a theoretical problem IMHO. Until recently (before SSD became affordable) the bottle neck was always the HDD and not the ethernet wire. Add into the equation cable quality, cable length and NIC in the PC, you will not even reach the theoretical maximum. With SSD (in raid) start paying extra for 10 gigabit Ethernet NICs and switches. Then the whole discussion shifts that an C7 or even the WRT series will not even suffice.
However I am in favor (biased) for an MT7621 based router for a cheap solution. Dual core, more RAM. A quad core ARM would be next (more expensive) up to x86 based for performance. If the file transfer is important enough and/or your NAS can handle it.
I can confirm that they can be found for a very cheap price, here in EU for about 75eur.
Maybe i'll buy one as well but i wouldn't have any use for it atm, i allready bought a few DIR-860L B1's last time and a Cisco SG-300-10PP... Well my girlfriend will kill me soon enough anyway !
Even with hardware NAT from OEM firmware no one is hitting 1,000 Gbps that I've seen. Most of the benchmarks, even the rigorous ones at smallnetbuilder are hitting 850-950 Gbps (simultaneous up/down is has ranged from 1,000-1,500 Gbps though).
The expectation is that the limit of "gigabit internet" is about 940Mbits down.
I wonder if Mikrotik hAP ac^2 is supported. (it's a 700MHz quad core arm with a 2x2 2.4GHz n and 2x2 5GHz ac), based on a recent ipq chipset; costs about $70
