Ubercart Stock Module

Hi,

I'm tired of searching and i can't find the answer for my problem so i decided to ask some help.

I have ubercart with marketplace V7.
I'm trying to find the best way to manage out_of_stock.

1º Method
- My problem with out_of_stock is that its not very easy to an user fulfill the stock amount, so if the user does not fulfill this the product will be always in stock and the decrease will not assume on this, so i can fix my problem with this module if:
1) Change the module so when creating a new product the stock is active and with value 1 (this is solve all my problems, but i can't figure out how to do it)
2) Make something that when creating a new product the user is forced to fulfill this stock and make it active.

2º Method
Since the 1º Method i didn't figured out i tried to do different and i think it's better but in fact i can't figure out how to do with rules
I created a custom field named stock and i make this field default by 1 (or can be change by user).
The problem is that on the rules i need to make one that when customer checkout complete it reduces the value of this custom field by how many products was bought and i can't do it... I can't figure out how do i found the field to reduce the amount.

Please help me with this, i can figure how to do it with views for both methods but i can't figure out the problems that i have.

Regards

UPDATE:
I found a code that can be inserted through DB query to insert new fields
insert into uc_product_stock(sku, nid , active, stock,threshold)
select model, nid, 1, 1, 1 from uc_products
where model NOT IN (select sku from uc_product_stock)
Anyway i don't know how to insert this on a rule, my ideia is on saving new content it runs this code to insert on database if not created this is possible?