Concrete blocks for walls and foundations — standard 440×215mm blocks.
A standard 440×215mm concrete block covers 0.0945 m², so you need about 10 blocks per square metre. Allow around 0.3kg of mortar per block for thin-joint bedding, or more for traditional 10mm mortar beds.
About 10 standard 440×215mm blocks per square metre, allowing for mortar joints.
Dense aggregate blocks suit load-bearing walls and foundations; lightweight (aerated) blocks insulate better and are easier to handle.
Yes — a damp-proof course between the foundation and the blockwork stops rising damp.