Hey, a friend of mine did a Sprint tri with a swim suit that had the thin straps and she seemed okay, not sure if the straps chafed but you could play it safe and put some bodyglide around them just in case. I had a suit like that for swim class and it ended up stretching after a while, so I would just say make sure you swim in it a few times and make sure it won't stretch in the strap area so that it gives you less support, particularly on the run. If you're bigger on top you could probably put a sports bra under it.

For such a short tri I think you'll be fine, no need to invest in specialized gear, but if you are doing several of them and think you'll continue, you might want to look into investing in some padded shorts or a padded suit.

K.