Vertex for Use Tax

There is a customer I implemented Vertex with. Do you have any issues? 

1.  Can we send Instant Invoices to Vertex from IFS.
     Examples Correction Invoices, Intercompany transactions, yearend bad debt write offs.
2.  Can we send use tax from IFS to Vertex
3.   Is there a way to prevent the print/send invoice portion of IFS to Vertex file send from duplicating if IFS session freezes.
4.  Three sites from one company.  Information not going into Vertex correctly.   They said it is the way our locations(sites) are setup.
5.  Issue with Credit Balances from RMA's , credit balances for negative sales remain out there until a great tax can net against it.."

Thanks for your help!