[kwlug-disc] GPL design question

[Insurance Squared Inc.]

I'm building a  web based php calculator that will become GPL'ed.

I need three things.  Input page, output page, and some calculations in 
between.  Oh, and they rely on some proprietary data tables of a small size.

What's the common way in GPL stuff to handle that framework from a 
design side?  And what's commonly accepted for handling small data tables?

 I'm thinking for the design, two ways I'm considering:
- I can have there components.  An input page (html), an output page 
(html) and a script The input page feeds the script, the script parses 
the output page and displays it on the fly.  That way users can just 
edit an input and output page, and done.
- Alternatively I can have a script with some html snippet files, like a 
header, body, footer, and so on.  That's what some stuff does I know, 
but seems less intuitive.

What's the common/preferred way when people need to edit the io pages 
for a web calculator?  Certainly not embed the html in the code :).  
I've done the first way in the past but don't see others using that.

Secondly, do I need to do a full workup of mysql, importing data into a 
database during setup, etc.?  Or can I get away with a flat file 
structure (it's not a lot of data).  Thoughts?  Users won't be likely 
changing data.

Thanks!

p.s. - this is a mortality calculator; type in your age and a few 
details about yourself and it'll tell you your life expectancy.  A US 
actuary has done an excel version, I'm creating a web version for them 
(and myself).  For my version, I've also got some mortality tables from 
the early 1900's and 1800's, so mine will also calculate your life 
expectancy if it was like 1880 today.