A wise detail to take into consideration: you should centrifuge your blood samples in order to separate the plasma from the red blood cells. I think you should always do so. If you want to conserve your samples for long term storage, then you can freeze both plasma (do not need ethanol), and red blood cells (with some ethanol) independently. Hope that helps.
For DNA extraction it is not necessary to centrifuge the blood samples. Indeed, you do not need a lot of blood for DNA analysis. If, however, you want to work with blood lipids, it is absolutely essential to separate plasma and red blood cells, remove air from plasma samples, and freeze as soon as possible. You will then also need a lot more blood (more than 2ml).