So, what's the minimum Size of a full-verified Node?

Some 10's of GB by just running parity --no-warp. Earlier this fall it was less than 20 GB, but the state is growing very fast. Currently, the raw historical block data containing the blocks and transactions is approximately 12-15GB in size and the latest state around 1-2GB.

But is this to be considered a full Ethereum node? Yes:

- It runs a full blockchain synchronization starting at genesis.

- It replays all transactions and executes all contracts.

- It recomputes the state for each block.

- It keeps all historical blocks on the disk.

- It keeps the most recent states on the disk and prunes ancient states.

Something an Ethereum client never does is deleting old blocks. This is a significant difference between Bitcoin and Ethereum because pruning a Bitcoin node does not leave any choice but removing old blocks. With this context available, it's easier to understand why users often think a pruned Ethereum node is not a full node. But now, dear reader, you know the opposite is true. :)