Hello Behemoth,
as much as I love PfSense, I see no big advantages of using it in a residential (private) environment (here come the haters...). Let me explain, I did try most of the things you're asking about myself a couple of months ago, I might relieve you from a short suffering.
Most of the info you can find online points towards PfSense in a business environment, even if not explicitly stated. In a "modern world" home network, you'd simply want to distribute internet access to all your devices and not fiddle with it too much if you don't have to. Why? Because there are no big advantages.
I have been running a PfSense box with an SSD on a "high-end" Intel Atom with two Intel gigabit network cards and 8gb of DDR3 memory (yep, it's is a dual-wan custom router test build, made for caching stuff). That means that it all comes down to the software and my internet connection, there shouldn't be any hardware bottlenecks. I know that my connection is really bad (6mbit/s) that's why I wanted to cache as much as possible. Turns out, there is not so much stuff that actually needs caching. Most of today's websites are dynamic and change often. True, you could cache them as well, but then you lose that dynamic aspect (think of looking at a 5 hour old Facebook timeline, even after you refresh the page for example).
Another thing you could try is to cache are advertisements, but these also switch around quite often. Another obstacle you will run into is that PfSense does not cache data being transmitted over SSL.
LEt me show you some scenarios where PfSense will excel any other (affordable!!!) router out there. Imagine you're a landlord of a 5 storey building and you're renting out apartments with a hardwired internet connection. In that case you'd put a PfSense box in the cellar and have it manage and distribute the available bandwidth around all tenants, depending on their current needs. This is called traffic shaping. PfSense does an amazing job with that.
Another example would be in an business environment, where you'd have to ensure a good connection for any sort of VIOP (voice over IP - Internet phones) client. In this case, PfSense can be configured to prefer any traffic coming from such a client, and in extreme cases, drop other traffic completely.
Coming back to to the you-as-landlord example: PfSense can help you cache large, static files. Windows updates for example. I heard that it should be possible to cache YouTube videos as well, but have fun configuring this.
PfSense is also great if you want to bundle two internet connections (for example from 2 different providers) and route traffic according to some of your custom rules. Browsing only through provider "A", FTP, VOIP and all other traffic through provider "B".
PfSense can also sense if one connection is experiencing problems and reroute all traffic to still guarantee a usable (albeit much slower) service.
Or, and that's where PfSense is originally originating from, you could build a super safe firewall with custom rules. However, this firewall will only make sure that intrusions won't happen. You'd still be vulnerable to some malware, as well a government privacy intrusions which occur later in the connection.
If you don't see yourself wanting to accomplish any of the examples in the scenarios, I would not touch PfSense for any other thing than curiosity.
I also experienced hardware incompatibilities with my motherboards fan controller, so that I had a pretty loud PfSense box.
MY TIP: Get a good DD-WRT router and spend a bit more money on that. The time you'll save will pay off (remember: Time is Money). But if you're still interested in networking as such, use that old computer and build yourself a small linux (Ubuntu) server (after you installed the DD-WRT). You can (yourself) have it do everything PfSense can do, but you'd be building and configuring the software yourself, from scratch. That means, you will pretty quick get a grasp and understanding of what's really going on.
Why Ubuntu? because you can find amazing documentation on the internet about anything you want to accomplish... routing, firwewalls, VPNs, proxies, caches... everything. Learning by doing. It's amazing.
@Dexter Kane: I'll nominate you for THE most patient man (or women) on the internet. You should be rewarded with an alcoholic beverage of your choice for explaining all this in detail.