Product sample request for sales lead

Hello everyone, we have a distillery operation and we are facing the following situation:
To promote sales we offer free samples of our products. Our salesmen should request the samples linked to one of their leads (no yet clients), so we can start an approval process to authorize the samples.
So far we have found that this procedure is the best way to go:

  1. Create a “Sales sample” Warehouse
  2. Modify doctype “Material Request” to add “Sample request” to the purpose list
  3. Add Salesmen “Request from” linked to logged salesmen
  4. Add a “depend on” field if Sample request is chosen to force “Sample warehouse”
  5. Make an approval workflow (I don’t know how to do it yet but I’m using only the logic)

I have a few doubts:

  1. Is there a better way to do it?
  2. Is it possible to add permissions to salespeople for doing this without opening another potential problem?

Thanks for your comments
José from El Salvador