I like that alot, great hardscape man!
I'm also doing a dry start with hc and dhg, (link in my signature), it's been going for a month now, and i have nice growth, and deep roots. I'm JONZING to fill it though! lol
It's ironic because I was looking at your journal right before I started my hardscape.
This is my personal opinion on filling it. Do it when you feel like it. HC grows more quickly submersed to begin with. I like to dry start to get it rooted as it's a pain to plant but I have yet to let a tank totally fill in. I actually like seeing it fill in underwater myself.
I would up your CO2 at first and have a 5-6 hour photoperiod to avoid algae. It takes time for HC to transition to immersed so you almost want to treat a dry start tank as though it has no plants. Then extend the photoperiod and dial down the CO2.