ad 1) not at all - create an additional page before the last one. If you want no further one, user buttonHide().
ad 2) Please us an array for the variables:
valueSum(array('E021','E022', 'E032','GO01'));
Note, that this will only (!) work, if E021 etc. are variables, not questions with multiple Items. If these question have more items, please write:
$sum = valueSum('E021') + valueSum('E022') + ...;