Barcode integration and product quantity not aligning with what i need

[TDdesigns]

Hi all.

I have a Shopify business where I hand make many different sublimation items and stickers.

Since starting 5 years ago I have always just made to order.

We also have one offs that sell online and at markets- last thing i want to do is sell something that has already sold the other way. 

Of late, we are starting to do markets and shows and we want to do many more so we wanted to implement barcodes to help know what we have on hand. That way when we get home after each event we don't have to do a full stocktake..... which is getting a bit much let alone when we start to do at least 1 event each weekend. 

We spoke to Shopify help, and they said to set all our inventory at 0, turn on keep selling when out of stock, and add it to the on-hand inventory when we have an item on hand. 

So we spent ages resetting all listings to 0.

Then we used 'EasyScan' to get barcodes and start that process. After issues there too we got the barcodes working and all seemed good...... until we tried to scan the barcodes and nothing out come up.
So we added one item to 'on hand' and it scanned..........
Turns out unless you have at least 1 in stock it wont scan. 
So then went back into shopify and some quantities have magically reappeared......

I am pulling my hair out and so tired after spending days on this and getting absolutely no where! 
Is it possible to 'continue selling when out of stock' via barcode or not? Am i wanting something too much and i have to go back to doing everything by hand and then add/delete from shopify..... 

Probably made no sense at all but if you have an idea what im on about please give me some ideas please!

ADDING- could this be possible by setting up 2 locations?
So one could be made to order which doesnt go out of stock so set to 999 and any that i have physical into a 'Market' location for what i physically have on hand? would that work?

[gr_trading]

Hi @TDdesigns 

Let me know if we understand it correct.

Your problem is barcode don't work if stock is 0 and if you uncheck the continue selling when out of stock then your product becomes unavailable if stock becomes 0??