Hi there,
Good luck on your first sprint tri. If the water is 70, they may not allow wetsuits, some races only allow wetsuits under 68 degrees.

If you wear a wetsuit, you can wear spandex shorts and a sports bra underneath and then just throw on a bike jersey for the bike/run. There are other threads on this topic too.
http://www.trifuel.com/node/4023
http://www.trifuel.com/forum/14603/first-him-what-to-wear
http://www.trifuel.com/forum/15289/tall-girl-with-big-boobs-what-to-wear...
http://www.trifuel.com/forum/13866/what-to-wear-for-1-2-im
http://www.trifuel.com/node/5737

Good luck as you count down to race day, I hope it goes well for you.

Ooops. Yes you are correct. My mistake!

Here is the rule.
4.4 Wet suits. Each age group participant shall be permitted to wear a wet suit without penalty in any event sanctioned by USA Triathlon up to and including a water temperature of 78 degrees Fahrenheit. When the water temperature is greater than 78 degrees, but less than 84 degrees Fahrenheit, age group participants may wear a wet suit at their own discretion, provided however that participants who wear a wet suit within this temperature range shall not be eligible for prizes or awards. Age group participants shall not wear wet suits in water temperatures equal to or greater than 84 degrees Fahrenheit. The wetsuit policy for elite athletes shall be determined by the USAT Athletes Advisory Council.

Agreed -- you probably don't wanna mess with a wetsuit if the water is around 70ish. Wear what's comfortable -- tri shorts and a dark colored running bra work well. Just remember that if you're putting on a tank top or jersey in T1, make sure it's loose enough to get on a wet body otherwise you'll waste time fighting with it to get it on.

Good luck on your first tri and let us know how it goes!