I will be traveling to Europe March 2-10, with a roundtrip to CDG in Paris as this is the only nonstop European destination from my hometown in the US. However, my intention is to visit London and then Budapest rather than France itself, since I've been to France multiple times in the past. I will be landing in CDG at about 8:25am on Saturday March 2 and my plan is to immediately go to London. My options are catching another flight from CDG or taking the train from Gare du Nord to St Pancreas. Here is where I would like some advice:
If I book a one-way to London how much time do you think I should give myself for the transfer process? Like 2 hours? 3 hours? I'm not sure if I land on Terminal 1 or Terminal 2. Similarly I don't know what terminal do flights to London take off from. If they are on the same terminal I would imagine I can skip customs and just transfer fairly quickly, right? if not then I would have to do customs and switch terminals plus go through security which takes time.
If I take the train, do you necessarily have to purchase your ticket in advance or can you purchase at the train station? I read somewhere that if you miss your train you can't just hop on the next one. I know I have to factor the time it takes to do customs at CDG, take the train to Paris, then do the check in and then take the London bound train. How many hours would be safe to allocate for this option?
I would appreciate your responses, and like I said I've been to Paris several times so I'm not worried about sightseeing there, I'm already spending 1 night at the end of the trip.