Some newbie questions

I have a couple of newbie questions regarding home recording. I hope
you bear with me, even if the questions seem silly and/or obvious :-)

I have been recording music (electric, bass and acoustic guitars) using
consumer level equipment (sound card integrated into my laptop and a
cheap mic that came with the laptop). I would, however, like to get
some better equipment.

Firstly, I've been thinking about starting with buying a Shure SM-57
microphone (seems suitable for my recording intentions). As I
understand, this microphone has balanced outputs. My consumer level
sound card's inputs are, of course, unbalanced. So my first question
is; can I connect a balanced output directly to an unbalanced input
(using a simple XLR-3.5mm adapter) or will this cause damage to the
equipment/produce tremedously poor signal quality?

Secondly, the mic input on my sound card has a built-in amplifier
which, I assume, isn't very good. So the second step would be to
purchase an exetrnal mic preamp. I am considering a Behringer MIC200.
This preamp accepts balanced XLR input (and hi impendance jack inputs
which I guess can receive input directly from an electric guitar?)
which works great with a Shure SM-57. The problem is that I still have
balanced XLR output which I want to send to my consumer level sound
card line input (not the mic input, right, since the signal already is
amplified?). So, the third step would be to purchase a sound card which
has balanced inputs (I'm considering an ESI Maya 44). Once I have these
three steps, I'm good to go, right? :-)

Finally, I have a question regarding signal level in consumer and pro
level equipment. Apparently, the nominal signal for consumer level
equipment is -10dBV and for pro level its 4dBm. Does this mean that if
I have a pro preamp which outputs signals for other pro equipment, the
signal will saturate the input on my consumer level sound card? Is that
the only problem or are there other issues with the signal levels?

I am very grateful for all answers, tips and suggestions!
/ David