The 88W8688 is supported by the Linux Libertas driver (see http://linuxwireless.org/en/users/Drivers/libertas As yet I haven't found out if the driver supports Access Point mode. There is at least one firmware module to be loaded. It should be possible to load the firmware in a platform independent way. I don't know the protocol for porting a Linux driver to FreeBSD. Having the sources for an already working driver would make the creation of a FreeBSD driver a fair bit easier than starting from scratch.
You should consider moving up to a machine with pci-e and higher bus speed. An Atom CPU is going to be a hindrance as you will be working it pretty hard while a 1066Mhz bus dual or quad core intel will easily have enough power to handle this load.
Maybe even more importantly, get GOOD nic cards not cheap broadcom cards. I like the intel pro cards, very fast and reliable.
Right now, it seems increasingly likely that I will just get a Firebox x700, but only if the Realtek Ethernet problems have been fixed. If possible I would use an old thin client off of eBay but 1. I'm not sure how easy it is to install alternative native OSes on it and 2. I don't see any that have dual Ethernet ports. Pity :(
…and preferably no moving parts. I wanted a PC ... to log to an HDD...
How does that correlate?
That's probably my pfSense noobness shining though. I was under the impression that the embedded version is less flexible in terms of lifetime read-writes; logging, package installation etc.
I'm not sure I understand what your question/concern is.
Putting this switch between your pfSense and your clients should of course work in a standard configuration.
Your clients can get IPs assigned by DHCP from your pfSense.
The question is: how does your configuration look like and will it work in that scenario.
(best anyone can answer with the given details: SRW224G4, pfSense, DHCP)