I used a turkey baster to remove the extra water and sprayed the AS and HC when it looked like it needed it. 2x's a day should be plenty. I'm new at the process too, so take my advise with a grain of salt.
I'm doing a little project in my garage with DSM and HC. I have an old 48" t8 and some tupperware with AS and HC clippings. I didn't plant anything, I just spread it out and let it do its thing. So far it's been 2 weeks and I'm starting to see it take off. Oh yeah, I have only sprayed it 2 times total. I'm trying to see if planting each stem and spraying it daily was worth it. So far it looks like it's not.
In regards to the backgrounds. I still think it's worth it to have them in. The plants will never cover the back completely. Unless you are do a moss wall or something similar. Keep up the good work. It's coming together nicely