The firetube looks really cool. I don't know if the tube really adds all that much: maybe its just a ploy to get newbs to buy it because *sarcasm* it is a tube preamp, and everyone knows that you can't make a good recording without a tube preamp*endsarcasm*. In the end though, check out the video and see if it is for you. I wouldn't buy it just for the tube, you can get an art tube preamp for $20-30 these days:
PreSonus
As for your original question, the firestudio's main advantage is the ability to use the lightpipe inputs and outputs. If you can use, then you have no need for a second unit because it can, with the lightpipe extensions, record 24 simultaneous tracks. However, the lightpipe units are more difficult to find and more expensive than adding a second unit.
The Firestudio project is a standard, sufficient setup for most homerecording people. The FP10 is basically the same thing. The Biggest difference is that the Firestudio Project (and the FS) has a firecontrol stereo mixer computer side. This allows you to create 4 separate stereo mixes to send to whatever you need. The FP10 sends out 1 stereo mix (maybe two). The Firestudio Project has LEDs for -40,-6, and Clip, as well as activation of Phantom power on every two channels. The FP10 activates Phantom Power on every 4 channels and has a single clip light. Other than that, they are generally the same. You need to judge if having the the Firestudio Project is worth the Extra $200. Also, sound quality of the preamps are negligible: they are the same preamps in all the presonus units. They are up to modern professional sound quality standards. They both have a single included headphone (1/4") port
What I would (which is what you wanted to do) do is get on the presonus forums and see if you can actually Daisy chain an FP10 and a Firestudio Project together.