I was going to suggest those bamboo torch type things as well. They're really cheap too - I think my DH picked up some at Bunnings a few years about for about $5/each.

My sister is having a beach wedding in October, and she's having silk frangipani flowers - very beachy!

What about taking some potted palm trees, for the background of where you will be standing (will the water be at your back, or will you be facing the water?). I think some companies hire potted palms, if you didn't want to buy them.

Re: chairs, I went to a wedding a few weekends ago where there were only chairs for the grandparents/preggie ladies - everybody else stood for the ceremony. It was only 30mins or so long, so fine to stand up for that long.