wow that was actually really helpful..... btw i actually main Ragna, so this info truly does pertain to me and is quite insightful. I will be sure to take it with a grain of salt as you said, but I must start somewhere, and im sure there are much worse ways i could go about performing blockstrings.
The way I see it, I have a number of options on ground mixups, as you have stated above. Special cancels are a possibility, as are gatlings into moves with positive frame advantages. My blockstring must end at some point however, and at that point it is advantageous to not leave your opponent too big of an opening to strike back. Certain specials are incredibly unsafe on block, but are not all bad so long as they are not routinely used. I've very often all around this site that mixups should keep the opponent guessing, and the blockstrings they stem from should reflect that fact. So I could go off of what you said, and end my blockstring a variety of ways: Dead Spike, Hell's Fang, an overhead, a low sweep, or even turn the blockstring into a two hit affair, switching from high, mid, and low periodically.
Slowly, this is starting to make more and more sense. It seems I am learning :D Now its time for practice