Regression analysis / Time series

Analysis tool: SPSS Description of analysis: Potentially two projects: 1) Regression analysis in SPSS: Aim is to understand what has triggered some people to buy X from year 1 to 2 2) Regression analysis / Time series in SPSS: What has triggered some people to buy X over 3 years time It would be good to know best approach for both scenarios, is it necessary to conduct both cases or would just one provide enough information to take a grounded decision? Extra notes: