Making a colums total (SUM) with Views
Your current configuration is doing the SUM of all numbers in that field but per views row, so you'd see numbers added up within each node if you had a multivalue field. 

To make it sum up across all results/nodes you need to remove the Sort criteria, that can throw aggregation off. 



I don't think your second question is making sense, you want to make a reference to a value calculated within views?  

Entityreference creates a list of entities, and the summed up value is not an entity, you can't reference it like that. You can create a Views block and show the summed up value on some content pages and wherever you need it. Is that what you're after?