Hello ixion - i have the same as you for Grid B, thought maybe that 13a went with 23d? 16a went with 9a (connection services???) . Don't know what 6d is or how it could connect with 24a.
In Grid D I have all the symbols - I've put a > in 8a? Same as you I don't understand what to do next?
The 2nd set might be the Roman numerals but I don't see any further yet!?
Found Grid E quite hard to complete too.