You are asking a lot here.

First you must use a iPad or tablet if you want to use a scanner.   Make sure you get the right one there is only one Bluetooth scanner that works.  I have used them with no issues as long as you follow the setup instructions.  Here is the hardware page for the iPad https://squareup.com/help/us/en/article/5084-supported-hardware-for-ipads  When you enter your inventory you provide the upc number.  You can do this by uploading the data via csv spreadsheet or directly.  If you enter it via the app you can scan in the upc numbers.

Yes inventory management works fine I use it for our fireworks stands.  Is it worth it.  It's free so yea.  

For my fireworks stands we just have a cash drawer,  It's not hooked up to square and we don't use a printer for reciepts.  Most don't care and if they want one we text or email it to them.  I use a wireless star printer and drawer for my car wash.  Works great and you can control your cash.  Know that you have to have a printer to control the cash drawer.  The signal is sent through the printer.  If you don't have a printer you will have to open you drawer manually.

I don't use the square stand, Needed something more portable.

Hope that helps.