Have a look at a HM training plan to see what sort of training you need to do for it. Obviously running in the morning helps getting the body used to it as most races are in the morning. You don't need to eat whilst running until you do longer runs but if you are worried take some jelly babies with you.
In the article SFF posted it says the following:
"Pistorius says he grabbed his gun from under his bed and screamed at the supposed intruder to get out. "
Now, if I would have been in Reevas place I would have shouted back. Something like " it's ok it's only me" which then should have triggered something in Pistorious to hold fire. After all she was with him in the appartment so it's not like she turned up in the middle of the night unexpectantly...
I do hope that he will get punished as he did kill her and nothing will bring her back. I can't imagine how her parents feel.