I need to cook spaghetti for about 70 people. How do I cook up the noodles that morning and avoid soggy or stuck together noodles? I am assuming my heating option at this event will be the portable tray pans with the little heating candle underneath. So, should I cook the noodles, cool with cold water, and add a little olive oil to keep from sticking? Then to heat back up slowly mix some of the hot noodle water back in? My plan was to make both spaghetti and alfredo also.
Liberal amounts of olive oil is a must. I'm not so sure about the idea of adding hot water to the precooked pasta. It is usually the other way around.
Some italian restaurants will pre-cook pasta al dente before the meal time rush, drain it, mix it with olive oil and then will dip it back into boiling water for a minute before draining and serving.
It sounds like you don't know what heating methods will be available at the event. I'd first recommend contacting the event organizer or whoever's in charge of where the event is, and double check if there's a warming kitchen.
If there is, I'd recommend following my advice in How do I cook and hold pasta for 200 people?
If you're really dealing with no heating other than chafing dishes, I would recommend switching from a strand pasta to something like ziti or penne, and making something more like a casserole. They can be served at a lower temperature than you can with strand pasta, as you don't have to worry about the pasta being able to be twirled on a fork.
You do still need to be concerned about the time in the 'food danger zone' of 40°F to 140°F (5°C to 60°C), so if you're really far from the place that you'll be serving at, and can't coordinate to be there within 30 minutes of the food being served, I'd plan for something closer to my previous answer:
Make the red sauce a day or two ahead of time, to avoid stressing out too much on the day of the event. You should also make sure that you have everything that you're going to need for transporting the food (see below)
Cook and shock the pasta. If it starts to clump together as it cools and dries, stir in a little bit of (preferably cold) sauce ... but barely enough to coat, and get it in the fridge. If you can, after about 15-20 minutes, get it out and give it a stir to try to break up any clumps that might have formed as it cooled. (this could also be done the day before, if you have sufficient fridge space) I would still recommend not using a strand pasta if at all possible)
The day of the event, make the alfredo and reheat the red sauce. Heat the sauces as hot as you can get them, in as few vessels as you can. (fewer vessels for a lower surface area, so it'll stay hot longer). Cap them well (avoid evaporative cooling), and get them into coolers** that you've prepared a heat of time (possibly with hot bricks in the bottom ... wrapped in a towel so they don't melt your cooler).
Get all of the chafing dishes lit with hot water in the bottom. (even better if you can call when you're leaving, and have someone else do it before you get there).
Stir the unsauced / barely sauced pasta to break up any clumps. (much easier if you do it before you're also slopping sauce all over the place)
About 15 minutes before you'll be serving, mix the hot sauce with the chilled pasta, and set it in the chafing dishes. Keep a lid on them until it's time to serve.
** If you don't have a large enough cooler, line a cardboard box with large towels, put the pot in it, then wrap the towels over ... and possibly throw a few more on top after putting it in your car)