OK.
In answer to your question - yes, the Behringer pieces are unnecessary. That means the compressor, the preamp and the mixer. Your interface and DAW will do everything the preamp and mixer will do, and I'd wager do it better than either of those Berhringers.
Read on for my reasoning on ditching the compressor:
With compression and tracking/mixing on a computer, you just don't need outboard compressors unless you're going for character pieces like:
http://www.americanmusical.com/Item...0HAMS0000&utm_source=froogle&utm_medium=feed&
or
http://www.sweetwater.com/store/detail/TLA50/
These sorts of compressors add their own (generally pleasing and musically desirable) character to the sound. That behringer will not do that. It will, at best, compress relatively cleanly (ie, without adding anything to the sound), and at worst add some sort of extra noise (based on the cost of the unit, it was manufactured with low quality parts and so there's most likely gonna be some ugliness added to the signal because that's just the way audio works...I ought to be able to give better reasoning but there it is) that you don't want in there.
There are lots of free vst compressors that do exactly what you would hope that Behringer would do, without having to add an extra piece of low quality gear to your signal chain.
Reaper, for example, which is free to try and cheap to buy, comes with an excellent compressor, Reacomp. Clean, plenty of really precise controls - once you learn it, it does exactly what you want and nothing else.
The other issue with using an outboard compressor in a digital system is that, if you compress on the way in, you're stuck with what you did.
Now, this is totally worth it if you
a) know exactly what you want the compressor to do to the sound before recording (which is something it generally takes years of practice for audio engineers to be able to do quickly, efficiently and correctly)
and
b) have a character piece like those I pointed out above.
Otherwise, there's just no point in compressing on the way in.
Using a plugin in the box leaves the option open for you to change your mind down the road during the mixing process.
The only reasons I could see for getting that behringer compressor are either if you are recording to a format where plugins aren't an option (ie analog or an ADAT/Hard disk recorder or something along those lines) and you absolutely need some compression and can't afford anything better or you're working live sound and absolutely need some compression and can't afford anything better.
All that being said, as you're looking at interfaces, are you planning on just recording your parts, or will you be recording the whole band (drummer included)?
If you're doing drums, you'll likely want something along the lines of that line 6. I haven't used it, but it's got eight preamps, so you're good to go (at least for a start).
Bear in mind that that Shure drum micing kit doesn't come with anything to capture cymbals and/or room sound. It only covers close mics on the kick, snare and two toms.
However, if your singer has a high quality mic from Blue, then boom, you got at least one overhead/room mic that'll work pretty well for you.
I might recommend scrapping all the mics you had initially listed and spending that money on one higher quality ldc or a higher quality pair of sdcs.
That (or those) in combination with the shure drum mic kit and your singer's mic should put you in the perfect position to be capable of recording drums, amps, vocals and any acoustic instrument you can think of.
Sorry for the length, just felt like typing for a while.
