Zoho One: books and inventory working together

Zoho One: books and inventory working together

Hi,
I was very pleased when I saw that in Zoho Inventory can now pull the orders from Woocommerce.
They are now fed in Inventory as Sales order and with choosing convert invoice as Instant Invoice I am getting the exact data as they appear in Woocommerce. 

These invoices now also appear in Books, which is just what I needed! 
However, as I can only use Instant Invoice manually, the invoices all have the date on which I am doing this and not the actual date of the sale. That is a bit of a bummer, but, well, not much I can do . The other option of converting invoices always results in rounding problems as Zoho rounding seems to be different from Woocommerce rounding.

I now have the following questions regarding books and inventory:

1. If I go to settings- general I see that I can tick a box for an Inventory Add-on

currently, I have not ticked that box. what will happen if I do? Will there be any changes in the invoices or items which I have currently in books? I am really scared that it will mess up everything.
The full use of inventory is sth. I will look at once I have finished setting up books with last year's data (which is not that easy as one may think, I have a lot of corrections and adjustments to make still)

2. the shipping fee
is there a way that the shipping fees can always have the standard rate of 20% ?
While I am correcting the invoices I have added from last year I noticed that the vat for this never shows (although it was in the .csv file, as did the discounts, fees and other stuff which did never show once uploaded)

3. scanning of receipts etc.
I read somewhere that the scanning is now free? Does that include scanning of documents/invoices?

Kind regards,
Sabine