Take a look at the HMDA guide: HMDA Getting It Right. The exemptions as they relate to purchasing loans are: if it is the purchase of an interest in a pool of loans or simply the purchase of the right to service the loans, you have get the exemption.
Appendix A has a discussion on what codes you should enter on your LAR. For example, you enter "0" "if you orginated or purchased a loan and did not sell it during that same year..." These items are also discussed in Appendix D - the Staff Commentary.
You can find this guide on the FFIEC web site. Hope that helps!