"We should just give each block weight and add cargo to the ship weight. Thus cargo ships need many thrusters..."
We could give PlexStore blocks a general 1m³ storage capacity and each block a compressed size to make some weight permanent (part of construction)
Computers mostly have their size for cooling and the interface, thus you could put 5 into one PlexStore block. You can also put many plants into one block.
But Thrusters, Power, Shields should take a full block.
Dunno about hulls. Maybe if they get a rename to hull-plates rather than hull-blocks, or if we get a space-compressing technology in a Plex-Store's description ...