I promise I'll read the docs, but I would greatly appreciate
a short road map for our very humble ambitions;
a small estore with
1) payment by CC (authorize.net) , paypal and check/mo

for our store, we've found that a simple linear function
cost = A * weight + B
works out very nicely .
for our 10 products of various weights
as long as the coefficients for "A" and "B"
can be set for 3 different shipping zones:
and everywhere else ( all by USPS btw)

So I'd like to have a "custom calc" of these shipping costs.
instead of going to the USPS server.

What modules need to be added/setup ?

Thank you,