BA600 (LHR-PSA) was cancelled due to weather (fog at Heathrow), and hence BA601 was cancelled as there was no aircraft to operate it. Generally, compensation is not payable for delays due to weather.
See here for baggage allowance:
https://www.iberia.com/luggage/allowance-in-hold/
If you are travelling on an IB5XXX flight and/or in transit between IB5XXX flights, the free baggage allowance will be one piece of baggage weighing 23 kg.
When the weight of the piece is more than 23 kg, every kilo over will be subject to a €12 surcharge, up to a maximum of 50 kg. The surcharge per additional piece is €25 payable at the airport plus €12 per kilo of the weight of that piece.
The policy of the operating company is that these surcharges for excess baggage weight or number of items apply to each section flown and not to trips (departure-arrival airport).