How were the first coins spendable? Apologies for my limited understanding, still learning.

According to https://en.bitcoin.it/wiki/Genesis_block:


  The first 50 BTC block reward went to address
  1A1zP1eP5QGefi2DMPTfTL5SLmv7DivfNa,[1] though this reward can't be
  spent due to a quirk in the way that the genesis block is expressed in
  the code.


I understand this to mean that the reward for mining the genesis block could not be spent.

To me this creates a catch-22 situation: If the first coins were not spendable, how was Satoshi be able to transfer the first 10 BTC for pizzas? Where did these first 10 BTC come from, if the first 50 BTC reward were not spendable? And how could then there be more coins, if you first need some transactions in order to fill the blocksize and mine the next block?
If the first coins were not spendable, how was Satoshi be able to transfer the first 10 BTC for pizzas?


It wasn't Satoshi (it was Laszlo Hanyecz, 1.5 years after the genesis block), it was 10000 BTC for 2 pizzas, and they were simply not the first coins.


  Where did these first 10 BTC come from, if the first 50 BTC reward were not spendable?


They were mined. Simply not in the first block.


  And how could then there be more coins, if you first need some transactions in order to fill the blocksize and mine the next block?


There is no such requirement. Blocks do not have to contain any transactions (apart from the coinbase transaction, which creates the new coins).