When you say Base Data Set @30 is 70 Gb, are you already including global road and global buildings?
In case no. Why Dataset is now sensibly bigger than before (about 15 Gb)? Only for rivers and lakes or terrain is more detailed or refined?
In case yes, i suppouse terrain remain the same as before.
No, that's why I wrote "additional 20 GB for the global road network ...".
It's bigger because although earth2 was made from 30m source data, it was resampled to around 76m to avoid having large data with SRTM sources that were stated to be 30m, but in fact heavily filtered and the actual resolution consequently lower.
There's a factor of 3x when getting to the next resolution level from 76m (to ~38m).
The new earth dataset (logically named earth7) is using some new DEM source data plus additional processing that justifies the need for for additional data, mainly in the nicest parts of the world. However, it's possible to constraint the data to use the coarser level and still have it looking good - and that's what we'll likely do, placing an option to have full resolution in world settings, but default it to a reduced one. That will lower the requirements for both users and servers.
There's now also a new dataset for water - encoding water level info for lakes and ground below the sea level, but that one is just around 2 GB.
Also those 15GB were without rivers (that came later).