I can answer the first part of your question: geopolitics. De Gaulle wanted to keep the six-member European Community (as it was known then) as a continental bloc that France would lead and that would act as a rival pole of power to the US and the Soviet Union. De Gaulle viewed Britain as a "Trojan Horse" of the US and thought British membership of the EEC would dilute that objective. He said as much in his press conference announcing his veto of British membership, saying that British accession would lead to a "colossal Atlantic Community dependent on and led by America which would soon absorb the European Community".

I'm relying on Jonathan Fenby's biography of De Gaulle here.