MAGENTO 1.7 tax and shipping rates configuration for imported orders

We import orders from AMAZON, EBAY, RATUKEN etc markets to our Magento 1.7 using 3rd party feed manager (like SHOPIFY etc.). We have customised magento admin grid which shows where imported orders come from (source) - eg AMAZON orders imported are listed with label AMAZON in admin grid "ORDER SOURCE" - we need to categorise orders from 3 or 4 new markets in this way. We use different shipping rates for different market place orders and need these configuring according to the rates and rules that are in place so that the correct information is shown on the Magento Invoice. We need issues fixing where incorrect SALES and SHIPPING TAX is added to Magento Invoice (wrong information shown, bad calculation). We need all invoices to show SUB TOTAL (inc tax), SHIPPING COST (inc tax) , TAX AMOUNT (20% of goods + shipping ), TOTAL AMOUNT inc tax We need this is set up for all invoices from all sources - there are different problems with orders from different markets such as AMAZOn and EBAY so need to check that all orders are corrected. We hope this will be easy for a Magento expert so please show us your track record with this kind of work. Our budget is around 100 usd