Technology

350mb/s symmetrical is very adequate for most households. If you have any trouble with speed, it's likely a priority queue problem or an issue within the network. (Basically, router/firewall or access point - which can be interference or capacity issues mainly).... Provided your equipment isn't bogged down, eg, CPU isn't fast enough to keep up. The best way to know on that last point is to check reviews where they test throughput. Having a gigabit ethernet port is nice, but if the router can only handle 200mb/s of traffic, you're going to have a bad time.

Starting from the top. Make sure your ISP will let you run in bridged mode. This can significantly reduce the work it needs to do, and increase the latency of requests (aka, ping time). Pfsense is very common, but I find it a bit cumbersome and I prefer opnsense myself. Try one, try the other... You don't even need to use it as your router, just load it up on a spare or old PC and go poke around the user interface... See if you can find all the settings for your internet connection, LAN connection, NAT/port forwarding, etc. Pretty much anything you would normally want to touch. See what you prefer. I find the user interfaces are some of the biggest differences between the two. For non-open source, there's some cheap but good vendors like mikrotik, but mikrotik tends to have a pretty steep learning curve, so buyer beware on that ubiquiti has some good options for small home environments too, like the UDR, which has all the fixings of a typical all in one router (switch, access point, etc) plus a ubiquiti controller, and it's quite capable. I like the UDR because it's not expensive (around $200) and has two PoE ports (out of the four total ports). This means you can add two access points to it. Throwing that together with a U6 access point for extending your wireless is a good solution and should come in under your $500 budget. The extra access point (or two, if you wish) will join the controller and work with the integrated ap, providing seamless roaming, as long as you turn on the appropriate settings. If you need more ports, there's a lot of ubiquiti switches to choose from that are well priced, so you can scale out from there if you want.

As far as pfsense/opnsense goes, it can be installed on anything with at least two ethernet ports. You can go pick up a small form factor off-lease workstation for a couple hundred, and drop in a second hand business/server grade ethernet card from eBay, and it will massively outperform the 1Gb/s ethernet interfaces.

If you want to go more piecemeal about it with pfsense/opnsense, there's plenty of good PoE gigabit switches out there, especially used business switches from HPE (I like the "1920s" model) or Aruba, even Cisco and juniper. Switches are usually pretty bullet proof unless you really abuse them, but companies don't like to have out of warranty stuff in their network, so the units get flooded onto the secondary markets after a while. PoE is good if you don't want to run power to access points, though you can also use PoE injectors... Speaking of access points, my favorite non-ubiquiti access point for the home is the Aruba instant-on series. They're managed from a free cloud portal, and I have yet to find a situation where they would do a great job. The only pinch is that when the internet goes down, you lose any ability to manage them. They're otherwise perfect. A step up from that (and not to be mistaken for it) is the Aruba instant series; they're a lot more expensive but locally managed and have a lot more settings.... It can be a lot more difficult to get up and running with the instant series if you're not completely familiar with networking, so buyer beware here too.

If your place is smaller and you only need one access point, the best option I've found, for price and performance is enGenius. The locally managed ones.... I haven't kept up with their product line, but I know they were moving to cloud management for most of their stuff. So finding the right access point may be a bit of a challenge. Also, I've used their access point systems (for multiple access points) and found it lacking, granted, that was several years ago now, so hopefully things improved, but I would recommend the Aruba instant-on for multiple access point systems over enGenius any day of the week. enGenius has the stand alone access point crown to me though.

For WiFi 6/6e/7, it will depend on your situation. If you're in a high density environment, you may get benefit from 6e/7.... If you're in the suburbs or in a more rural situation, 6 is going to be fine. Just make sure you're buying dual band access points. The big benefit for 6e is that you gain access to the 6Ghz band, which is only really helpful if your local 5Ghz band is overcrowded, like in the case of a high-rise apartment (even then, it may not be all too helpful), and WiFi 7 builds on this with some multiple access performance improvements as the key features. Meaning fewer slowdowns from many things on the WiFi at once. WiFi 6 already has some multiple access improvements, most notably MU-MIMO, so, I wouldn't worry about it too much. 6e is going to simply reduce the chances that you have to share a 5/6Ghz channel with anyone else. The issue with 6ghz is that not all devices support it (laptops, cellphones, etc), and certainly no electronics (IoT stuff, printers, TVs, etc) will support it.

Personally, if you're not into networking as a hobby or a full time job, then I'd usually point you at the ubiquiti UDR, and add one or two access points depending on coverage requirements. Either going for the U6+ (if you absolutely need to save money), the U6 pro for ceiling mount, or the U6 mesh if you need to plug it in and place it on a surface (The mesh is a bit more money due to it being so compact). For more hardwired ports, if you want more access points or something, maybe the Lite 8 PoE.... There's also the flex mini if you only need a handful of extra ports.

If you want something more challenging, using an opnsense router of custom built off the shelf computer parts is a good option, paired with an eBay find of a HPE 1920s with PoE and a couple of Aruba instant-on AP22's or something would be spectacular, but a bit more involved, and likely a bit more pricy, since I'm not sure how well the instant-on AP's fare in secondary markets (I'm not sure if Aruba will let you register a used access point into the cloud controller).

The ubiquiti solution has legs but you'll be limited by the fact that it only has 1Gbps ports... It's powerful enough that you can fully use those ports, but it will never go faster than 1G.

I hope that helps. I know it's a lot of information to process. I don't know your situation and I can be much more specific about what to use without getting into a lot of detail about your situation. I don't want you to have to post that information publically on the internet, so I wanted to give you the information to make an informed decision. I hope I have done that, and I wish you the best of luck with your future network.