Yes, you can enable clients to buy only simple or only configurable products as well all types of products. Follow the link to learn about additional possibilities.

Yes, the statistics can be seen in the admin panel. The report includes such showings as operation name, comment, customer's name, email, operation value, remaining credit, operation date and website (in case you have several store views) columns. Read on to see an example.

For this, you need to create a 'Store Credit' product supplying it with all essential information. See how to make it correctly in the compelte answer.