Application using PostgreSQL as a back end (experienced programmers please)

Hi:

I'm an accountant, not a programmer, but I've written a time keeping
application using Visual Basic for Applications and Microsoft Access. I've
also done some VBA programming in Microsoft Excel.

I eventually (some time in the distant future) want to write a Canadian open
source income tax program for individuals using PostgreSQL as a back end and
a GUI front end.

In the meantime (to teach myself), I want to create a program to keep track
of the cost basis of shares traded on the North American stock exchanges. I
would use this program for work, to keep track for income tax purposes, of
the cost of shares over time to our clients. Something we currently make do
with using a flat file database in MS Excel.

My Problem:

I have introductory books on Python, Perl and Tcl/Tk. I feel comfortable
setting up the database in PostgreSQL, but in creating the GUI front end,
I'm not sure how to invest my time. Should I use Tcl/Tk, Python with Tkinter
or wxPython (using BOA Constructor?), Perl with ???. Which will get me most
productive in the shortest amount of time (considering I'm not a
programmer). Which combination works best with PostgreSQL? I expect the
income tax program to be computationally intensive but I also expect most of
this computation to take place in PostgreSQL and not the front end.

I will be investing a significant amount of my spare time into these
projects over the next few years and would be grateful for any direction
from experienced programmers.

Regards,
Bill Dika