Custom Need

I tried FA, is excelent, but for at implemation in my country I need some change:

1.- Invoice (Various series, example, Sera A, B, C, D, etc.) Each serie need to have the own consecutive number.
2.- Sales Person, I need to change the sales person in the moment I made the Invoice, right now the sale person in in the branch, this is ok, but I need the option to change then in the moment that make the Inmvoice.
3.- Tax, In my country have 3 tyoe of tax, one is the sales tax like other country, but We have 2 tax, one is Municipal tax and the other is like federal tax, both tax is 1% and this tax is include in the base price. For example is I will buy some device to 100.00 + tax (15%), the total price is 115.00, 15 is sales tax, 1 is Muniipal tax and the other 1 is federal tax, some time the customer just pay 113.00 because they retain the federal tax and municipal tax.
4.- Currency, I need to change the currency in the moment that i make the invoice, because some time I made the invoice to the same customer in local curency and other time in US$. Also I need to display all report in the currency that I chose in the moment, I need a combo like option for curency to display the report.