1)I was reading over some of the threads about stretching, and I got the impression that if the duration between stretching and competition is short that it can negatively effect performance. Is this true? If it is, then how long should the duration between stretching and competing be, and are there any particular types of stretches I should avoid?
It really matters what type of stretching you're referring to. If you're referring to static stretching then yeah, it would affect performance since it relaxes muscles. Dynamic stretching and form drills are OK.
2) I don't really like to lift weights, but I know that doing it will help out my speed a lot at this point. Can anyone suggest a fairly relaxed (I'm thinking 3 days a week) weight routine that I can do after my daily practice?
One OL, one squatting movement and maybe an aux movement like RDL's or Bench Press after your HARD days (not just after any day).
3) I've noticed that my legs sometimes feel tired as I'm getting ready to run the 400m, which is normally the last race I run in the day. I'm thinking that eating something that has a lot of simple sugars in it between my 400m and whatever I run before it might help out with this. Would it?
I doubt it. Simple sugars give you a high that when you're result in you crashing like no other. If you're eating throughout the meet and eating the right foods (mainly carbs) everyday then the day of the meet you shouldn't have to worry too much about what you eat, but rather just eat something to KEEP you fueled during the meet, not something to FUEL YOU UP during the meet.