London Paddington.
Depends where in Wales you want to go... Trains can be taken from London to Cardiff in the South, or through Bangor and Holyhead in the North. You could also make an internal flight to Cardiff. Or drive, or take a bus.
Take a train from London Waterloo station.
Take a train from Paddington Station
Like literally 5-10 minutes, it's not long at all
No, as the Tube (the London Underground) does not run outside the City of London. You could however use the Tube to travel to Paddington Station and catch a train to Cardiff. The journey would take approximately 2 hours if travelling during the day and may be of longer duration in the evening.
Not directly, you have to go to the train station in London Paddington and take a connection train from there.
The quickest way is to take a train from Euston Station.
Direct trains take around 2 hours 5 minutes.
30 minutes if there are no issues in the London station
Take the train from Cardiff Central to London Paddington, take the Circle Line to Victoria station, and catch the Gatwick Express to Gatwick Airport.
It takes 24 montths
To travel from London to the Southampton cruise terminal, you can take a train from London Waterloo station to Southampton Central station. From there, you can either take a taxi or a bus to the cruise terminal. The journey takes approximately 1.5 to 2 hours by train.