If not disturbing.. i want to say my opinion also.

If user doesnt have an account and choose a subscription:

standard fields for account creating: Name,Email,Username,Password,Verify Password:

then Invoicing fields :

An option to choose A- normal person invoice B- company invoice (A could be default- and B if users clicks a radio button)

For : A - name (could be copied from register fields), and some other fields like adress etc (we cand delete or rename them- it's not a problem)

For B - Company name, adress, etc (i think we can create some fields in tables and rename them as we want so we can use the tags in invoicing template. (for me would be better if i could add fields alone because the laws from my country demands some fields in invoice like : VAT- but in my country are companies that are not vat registered - i mean they have only the number without country code.. anyway.. here i can add them... hope.

and now: If subscription price is 0 - no more fields for INVOICING .. only the standard account creating fields

Would be a plus... a captcha plugin in the future.
Also ... the INVOICE fields to appear everytime when a regsitred users choose a subscription.