This is your first Tri, right?
Use whichever shoes you think you'd be happiest in, put them on before you get on the bike and take them off after you get back to your transition spot. Don't worry about how long it takes you to put them on and off. Your first Tri should be about having fun and finishing.
On that same note, if you take a tube/flat fixin's with you, the worst thing that will happen is that you will be annoyed by it in your jersey. If you don't, the worst thing that will happen is that you will flat and may not finish your race. I would say that while the consequences are greater for not having that stuff with you, it's much less likely to happen on such a short race so I would tend leave it behind. But if it's really important to you to finish, then you should take it with you.
Living life like there's no tomorrow.
http://gorgebikefitter.com/
2007 Look Dura Ace
2010 Custom Tonic cross with discs, SRAM
2012 Moots YBB 2 x 10 Shimano XTR
2014 Soma B-Side SS