How to implement VAT declaration?

[Valdis Vītoliņš]

One of regularly boring issue for business accountants in Latvia is
providing VAT tax declarations.
So, I have to implement solution for this.

In Latvia there are 3 VAT taxes: 0%, 10% and 21%, though each of them
can be applied by different rates.
So there are generally (for most of businesses) following cases:
0%
10% not charged (amount is 0%, but it is not the same as simple 0%)
10% 50% charged
10% fully charged
21% not charged
21% 50% charged
21% fully charged

For each of cases summary VAT for declaration period should be counted
separately.

It seems to me, it should be implemented as plain list of different
taxes, and attach each of them to separated account. 
Then I should create guile report and look for each account and sum
transaction values for given time period.

Following questions appear:
1. Is this the best approach or there are more sophisticated approaches
available?
2. Is there some info, how to implement dialog window to enter
parameters for report generation?
3. Is there some example/guide how to sum account transactions?
3. Is it possible to create tax entries using file creation wizard? Is
XML schema for xea files?
(I tried to add elements from saved file but did not succeed).

Thanks in advance,
Valdis