svpii Re Eurostar I would suggest buying your tickets in Paris, they are generally slightly cheaper than London.

One possible exception is a two for one promotion that has been running for some time in the UK - not sure if it's still on, the website should offer all details.

If you're planning on going to Wales and need to stop in Cardiff on your way stay at the Big Sleep Hotel - book the penthouse suite, a steal at £85 (fun property, partly owned by John Malkovich, if a reference )

Regarding Paris, plenty of advice already, let me know if you need any specifics re shopping/restaurants/etc..