Install method: hard drive vs flash, and some wireless interface advice

[De1taE1even]

Hey everyone, newbie here with a couple basic questions.  I have some spare parts from an older microserver build that I'd like to dedicate to a pfSense/OpenVPN build.  I have the following parts already:
AsRock Q1900-ITX motherboard
Norco ITX-S4 case with power supply
4 GB (2x2) DDR3 RAM left from a macbook pro upgrade

Here's what I'm planning on buying:
dual nic card: The AsRock mobo has a pcie 2.0x1 slot so I was leaning towards an Intel PRO/1000, but I'm all about other suggestions.
wifi nic or AP: See question below

The one thing I don't have is a small spare hard drive.  I could go buy a small ssd but that seems like overkill.  Is there any disadvantage to running pfSense off of a USB 3.0 thumb drive (I ask because I already have one).  If there are performance/software advantages to running off a ssd I'll go that route since small ones are pretty cheap these days.  I want the set up to be as performant as possible given the hardware I already have.

Also one question regarding wifi.  That AsRock mobo has a mini pci-e slot on it that I was thinking about using for a wifi nic.  I am also considering a Ubiquity AP since they seem pretty popular for use with pfSense.  It's pretty obvious to me that the Ubiquity device would be the better choice, but how much better?  Is using a mini-pcie card not advised?

Thanks everyone, I'm anxious to get started!

[coolspot]

I was using a HP 360T Dual Gigabit Ethernet Card and it worked very well with pfSense. The HP card has an Intel 82571EB chip. Specifications are here:

http://h18000.www1.hp.com/products/quickspecs/archives_Division/12563_div_v2/12563_div.HTML

You can get this card on eBay for $25 or less.

[De1taE1even]

Thanks!  I ended up buying an HP card yesterday that I'm pretty sure is the 4-port version of the one you suggested.  I'm going to start off with a flash-based build for now, and only install to a hard drive if I feel the need down the road.