1) the code:
<?php echo(($yourCartName->TotalColumn("Weight") < 1)?1:$yourCartName->TotalColumn("Weight")); ?>
is used for the weight setting in the shipping lookup server behavior.
2) The select list to chose the shipping type should be added to the checkout form.
3) you need to add a set session value behavior to the confirm page. open the confirm page, go to the server behaviors tab click the plus button and select eCart -> General -> Set Session Value.
Set the trigger to any form post.
for the name, enter:
for the value, click the lightning bolt icon and select the USPS_Service form element.
that _could_ be done, but will take a fair bit of hand coding to accomplish