Some notes on this.
First, most multichannel interfaces today sends each channel separarately. This goes for both USB and Firewire. One marker to look for is that it uses USB2 as the older USB has bandwidth for only 2 in and 2 out. Do check out some alternatives and then come back here and we can guide you. Start out with the assumption that it will work and once you have a short-list come back for verification.
The people at GC are not necessarily very knowledgeable. I would not put too much weight on what they say. Also remember that they will never (that is NEVER ever) recommend anything they cannot quickly shift out to you from stock, they are salesmen firstly going on commission.
You can definitely use a laptop and record directly to the in-built harddrive. I have done this for at least five years often with up to 16 channels. It is not the optimum but good enough (like I would not have much advantage of a Ferrari in normal rush hour traffice, will not get there faster). Once recording has started there is very little activity from the operating system towards the drive. Just remember to turn off internet and antivirus while recording and you will be fine to go. In my experience it is a convenience to divide the drive into two partitions, using one of them for audio files. Not strictly necessary though.
But again, some laptops simply work better and some worse. You simply have to try it.
It used to be that Firewire was superior to USB, but the market now is moving towards USB2. One reason is that many modern machidnes, including Macs, does not carry firewire anymore. Basically USB2 is good enough so why have things that simply increase the price.
As said before Firewire comes in 4,6 and 9 pin varieties. All you need to connect a firewire audio interface is the correct type of cable. There are however very few portables that can supply power over the firewire cable to the interface, so expect a separate power supply. For the really technically interested, the higher speed firewire comes only on the 9pin variety, but it automatically "shifts down" if the audio interface cannot support the higher speed. Again for most users you will not need it (no need of Ferrari).
Good luck, the search for your perfect interface is here.
// Gunnar