So I finally was able to look at your PDF and the scope is bigger than just doing the WIFI setup. Some points:
1. All this screen rotation business I'm guessing you are handling that on your side, otherwise would need a lot more detail.
2. The video splash can be done (But still maybe a second or two of messages that can't be removed without actually modifying the kernel, I'd need to look into it). The pi can only play H.264 video encapsulated in a MP4.
3. Heads up: all of the network needs to be managed via Network Manager or WICD (trying to write scripts to fight with iwconfig/ifconfig/ifup/ifown/hostapd will only end up in pain and basically rewriting WICD). There's already a PHP DBUS API that can be used to talk to either of them.
4. There are other considerations that aren't in your PDF but that you must have otherwise your product is likely to fail sooner or later:
- Mount the Raspberry pi filesystem as read only, this will prevent the SD card to wear quickly and the filesystem to corrupt on power loss (really this is a must have otherwise the PI will eat the SD cards)
- Activate the pi watchdog so that it'll auto reboot in case of lookups.
I'm aware that I'm above your stated budged but you project IS complex and I don't think you'll find anyone that is actually knowledgeable to be able to deliver, willing to do it for cheap (you seem to have already learned that with a past contractor, there's already a guy promising to do it in 3 days which is basically impossible)