Sue,
Sounds like you have a solid running base and training schedule that you're using.  You will learn each time you go out for a run.  Personally, I cannot handle solid foods before a run.  Try to experiment on your long runs that you're doing now. 
Pre:  I use gels, sports drinks, and water.  I switched from Gu, simple sugar, to Hammer gel, complex carbs.  The Hammer gel helped me feel consistent during the run rather than having peaks and valleys.

Drinking lots of water in the days leading up to your run will help prevent dehydration.  Using the last table at aid stations will be less crowded.  Walking through some aid stations might be a necessity.  Depending on how you plan on replacing calories, you may want to carry enough gel for every 40-45 minutes if that is your sole source.

If the weather is predicted to be cool in the morning and warm up, you may want to wear something that you can throw away.  Old shirts and tee-shirts that you do not want any more are good for this purpose.  Some races take throw-aways to Goodwill stores. 

Unless you're set on performing at a certain time, I would go out and enjoy this run.  Keep yourself on track based on how you feel.  Definitely keep on track for the first half and then when you're at mile 20, running the last 6 miles is just like doing a 10k.  A lot of people hit a wall between mile 17-19.  Be mentally ready for your "wall" and know that you can push through it. 

Post:  make sure to eat and drink after your run.  Protein and carbs are good.  Massages can be good too! 

Going to the bathroom?  Again, may be dependent on how much you drink and the weather for the day.  Electrolytes are a must on hot days to help prevent muscle cramping.

Those are my initial thoughts....makes you think of a lot of other questions, I'm sure!

Jennifer

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