I was curious about feature size (e.g. wire width). The number of transistors can actually be found in some datasheets (don't remember exactly which manufacturer published it though).
A 2-input TTL NAND gate usually consists of 5 transistors:
Two multi-emitter transistors (counted as two separate transistors here)
One phase splitter transistor.
One pull-down transistor.
One output transistor.
The multi-emitter transistors are easy to make on-chip and are a clever way of getting two inputs into one 'device'. For a 7400 that was 4 sections x 5 transistors per section = 20 transistors, total.
NAND was the fundamental block in TTL; in the earlier RTL, NOR was the fundamental block - and used only 2 transistors, but needed resistors for the inputs and as the load pull-up. Power hungry and slow as a result.
