Hello halfway,
Thanks for the video, it was very informative. I'm not familiar with 'silica rock" I did a quick search and I didn't find the answer. Is silica rock porous or solid? I don't believe the the residual water that's left at the bottom when drained will be a problem, but rather an asset. The roots that hang down out of the baskets will dry out much faster than the ones in the
growing medium. Therefore if they can get access to a water supply (depending on flooding cycles) it would be a benefit. In fact, if it were me I would want at least about an inch of water left at the bottom when drained (at least enough to submerge air stones). Also I would suggest to put the air stones (currently in the reservoir) in the growing chamber with the roots. Any roots that may be submerges for long periods of time will benefit from the direct air bubbles.
Looking forward to seeing the plants grow!!!