Doing your own demos and EPs has its advantages. Time and money is the main one. Well if you already have some mics and a mixer with direct outs/inserts and your a standard band (ie, 2 guitars, vocalist, drums, bass, etc..) you could get by on that firewire 410. The quality in comparison to the studio could be comprimised (depending on the studios gear they have) but you will have more time to track stuff right, which could ultimately be better quality too?
The only thing about working on your own mixes, depending who edits it from your band, will more or less be biased to their part in the mix than others in the band

. But it doesn't happen all the time, its just something to be aware of if your going to mix your own band.
A basic setup could be, get some software (n-track is a good one for free if you haven't got one better than that already), a mixer with direct outs and or insterts (or some seperate mic pres a budget decent one is the Behringer
ADA8000 ) and some mics and obviously your instruments and amps.
The extra pres are if you want to mic up say your drum kit fully which would require atleast 4 mics for a decent sound, you'd run them from an external preamplifier such as the ADA8000 or mixer into the 1/4" jacks on the back of the firewire 410. Note, with the ADA8000, you'd need to get an XLR to TRS/TS cable to run it into the 410's line inputs.
Then use the preamps in the 410 for everything that only requires two or less inputs at a time (ie, vox, guitars, etc..) and multitrack everything one at a time.
That might take a bit of time to absorb, but not knowing your budget, i can't really give you a clear realistic idea of what you could have. See how you go, it might seem expensive now if your on a tight budget, but in the long run it would turn out better (with experience, time and gear).