Update time!
My planters are doing great, and growing in really nicely. I worried about the saltwater splash, but it hasn't been an issue at all. Also worried about the tipping, but even with a pool full of teenage boys it hasn't been an issue, not even a close call. We filled the bottom with broken up cinder blocks, so while it's certainly possible to tip them, you would really have to be trying. These take full sun all day, and we get to 100+ on a regular basis so I was also concerned I would lose some of the plants, but they're all still hanging in there in various forms of thriving.
The silver falls dichondra is my absolute favorite, I love how it's cascading around the planters. Not fussy at all, super easy to take care of, I find it soothing to untangle the little tendrils.
The hypoestes has faded to mostly green, and I think I should have planted something a little larger to help support the lemon grass. It was good that the lemon grass provided some shade as without it I think the sun would have killed these off. Lesson learned for next year. Maybe some begonias will fare better.
The lemon grass is doing well, even in our 100 degree heat. I do have to water it daily, sometimes twice a day when we're well over 100. It likes more water than the hypoestes and dichondra, so I made the dirt shallower in the center so it gets more water than the other two and that seems to be working well.