As far as your questions go:
- travel time should be within 1 hour from Amsterdam City Center.
You didn't specify whether you'd like to limit your mode of transport to public transport, so I'll just make that assumption for the time being. Your best bet is probably Zandvoort, dead west of Amsterdam city. From Amsterdam Central station, there is a direct train that will take you "Zandvoort aan Zee" station (literally translation: Zandvoort at the sea) in 30 minutes, which runs twice an hour. A single journey (2nd class) will set you back €5.30, whereas a return trip is simply double that amount. From that station it's only a short stroll to the beach.
You can plan your train trip using the website of the Nederlandse Spoorwegen (NS in short, translated: Dutch railways). It's availabe in English. Be sure to also check out 9292ov.nl (also available in English) if you'd like to include buses, trams etc as transport options too.
An alternative coastal beach, close to Zandvoort, is Bloemendaal. It has its own train station, but in order to access its beach it's easier to go to Zandvoort and take a bus from there.
If you're somewhat flexible with your 1 hour requirement, you could also check out "IJmuiden aan Zee" and "Wijk aan Zee". These two are close to each other but a little further north along the coast. Expect a travel time of up to an hour and a half.
Finally, if you'd rather stay close the 'home': Amsterdam has a few urban beaches too. I've never been there myself though, but definitely have a read through them on Amsterdam city's website (in English). The aforementioned coastal beaches are also described there.
- hip and happening crowd :-)
- Any special events going on would be an added plus.
I'll try to answer these in one go: on 8 November Zandvoort there's a big event happening on the local racing circuit, called Zandvoort 500 WEK (in English, WEK = Winter Endurance Championship). I'm not a big autosport fan, so I can't really comment on the crowd and its hipness factor. It's a free event though, so it may very well be worth considering. I'll leave that up to you.
For a full overview of all events in Zandvoort, have a look here (in English).
Other than that, there's probably not too much going on (it didn't check for all locations though). It's currently autumn in the Netherlands, so expect fairly cold, windy weather and rainfall. According to the extended forecast you should be prepared to face cloudy weather with a temperature of 6-10°C and some showers on the dates you mention. Be mindful of the added wind chill if you decide to go to one of the coastal beaches, although it seems like it shouldn't be too windy between 8-11 November.