First, check the Ethernet WAN cable. The ISP generally provides you a copper handoff to your router and that cable could be bad. That would make the most sense at this point since one bad conductor would limit you to 100Mbs.
I'd then try a direct connection with the laptop via Ethernet cable to the ISP copper handoff bypassing your router. You should be getting at least 900Mbs at that point.
There's this thing called google. People don't need to be spoonfed everything. The OP didn't even had the right questions. He didn't specify what speeds were required. A simple Edgerouter ER-X would be a better choice at anything under 200Mbs. Anything that didn't have WiFi would be a better router. WiFi is best done with AP's .
20 years as a network professional just makes me superior on the topic of network to the average person asking network questions here -- it's not a complex. Sorry if it makes you feel inferior.
I'm a networking engineer with 20+ yrs experience. I don't reference my background unless challenged. I give the best advice that I can in these forums since I see them as a sea of ignorance. Most people aren't network professionals and make very poor choices because of marketing and consumer availability. They then come back on the forums and complain about issues that exist because of their poor choices in gear.
Examples:
Why is my latency so high? Because you didn't get a router capable of QoS and are suffering from network congestion.
I need a new router because my WiFi doesn't reach the other end of my large house. That's because you should have purchased AP's and not relied on a single wireless source built into a router.
Why is my $80 all in one device locking up every day? Because it's a poorly manufactured all in one device.
The list goes on.
Just because nobody's asked -- how does one accidentally snap a cable in an enclosed box like that?
For me the answer would be no because I have a very specific idea what a router is and what it should do and that does NOT include WiFi. What's the throughput (with firewall/nat enabled)? Does it support QoS algorithms like FQ_CODEL or CAKE (and at what speed)? What are the firewall capabilities? Does it support DNS proxy? What are the VPN capabilities?
If you want WiFI, get an AP.
The connection from SW-A to SW-B should be a VLAN trunk -- ie tagged (all vlans assigned assigned would normally be the default). VLANs have to be defined on both switches.
The connection from SW-A to the router would also be configured as a VLAN trunk - ie tagged.
The only difference is how the router would be configured. From a Juniper/Cisco perspective, you would create subinterfaces for each tagged VLAN and assigned them the VLAN Id's of the tagged ports. Each subinterface would have an IP address corresponding to the network's default gateway. I'm not sure if the PFSense is different -- I never use this software for a router.
VLAN 1 is normally considered special because it would be the native VLAN on most switches so would be an untagged VLAN. If this is unintended, the easiest thing would be to change the VLAN number and tag it. Alternatively if the switch and router allow it, simply change the native VLAN to something besides 1. It it's intentional then do nothing.