Advice for a novice on making ambitious cross-platform GUI app

[Chelonian]

I'm considering trying to learn Python for a specific reason, and
hoped the group might help me get a sense for whether it would be worth
my time.  The situation...

Me:  total beginner w/ a sense of  programming basics and 1 week
familiarizing myself with Python world.  Use WinXP.  Got Python 2.5.
Fooled around in IDLE, made "hello world!" and one which takes user
input and tracks a string or two.

Project:  ambitious GUI program for Win/Mac/Linux.  Target user:
average person.  App to look elegant, and be intuitive, responsive,
exectuable, have its own icon, etc.  Needs to store user info in large
database for the long term, run in the background and pop up at
assigned times.  There are needs for graphing, data analysis, file
management, word processing, text processing, web synchronization, etc.
 It would have to look like commercial software, though it may turn out
to be free open source.  It's envisioned as a pretty tall order, thus
my wonder if I'm delusional in thinking I have any hope to accomplish
this.

To begin, I have decided on wxPython as the GUI toolkit.  Have also
begun trying the SPE editor with wxGlade as the GUI builder, and have
made a few line program to create a window.  Lastly, I have used py2exe
to turn that into an executable file with its library files for running
on computers without Python installed or without the wxPython
libraries.

I have read FAQs and looked into it.  Remaining questions are:

Can Python *alone* produce something like what I've described?  Or
would I have to have some parts written in C?  Or is Python really not
best-suited to these needs?

Is using SPE with wxGlade a good choice?  What about Boa Constructor?

Is it something one person could do over the course of a year or so,
working say 10 hours a week on it?  Or is this really out of reach of
anyone other than a hardcore programmer or even a team of them?

If I write it using Python 2.5 and wxPython, do I have to use py2app or
something to create an executable and necessary library files so it
will run on Mac?  (Because of wxPython's libraries, which the Mac
won't have?).  

Thanks for any thoughts you might share.