My family of 6 are planning a trip to California,we are looking at the Orange Co. area. What is the weather usually like the first 2 weeks in November.Also is Belmont Shore,Long Beach a good base, we plan on visiting Valencia,San Diego and Anaheim.

The weather in November is usually quite pleasant. It's fallish for California and the days will be sunny and the nights will be cool. You just layer your clothes for your day tours(many people are still wearing shorts). You can go to the beach and lay out on most days, but the water is too chilly for swimming. You can expect daytime temps in the high 60's to low 70's.
Belmont Shore is a good location right in the middle for where you want to travel. You are close to both East/West Frwy(405) and North/South(110/710)Frwys.
Enjoy!!!

I would actually suggest staying in the Anaheim Area if you are going to do only 1 city as a Base. Belmont Shores is between Valencia and Anaheim but San Diego is quite a ways and you will be on the road for a long time if you try to do a day trip to San Diego. In Anaheim you are about 1.5 hours away from Valencia and San Diego depending on traffic, making a day trip a little simpler.

Depending on what your plans are in San Diego and Valencia I would even suggest to stay a night or two at each of these as well as in Anaheim.

The others got the weather right. Belmont Shores is a really nice area with a lot of good neighborhood restaurants. I think it's a lot more pleasant and less touristy than Anaheim. I don't think it will take much longer to get to San Diego from Belmont Shores than it will from Anaheim. You're right on the edge of Orange county and you just get on the 405 freeway and head south.

I second the suggestion to stay in Anaheim,

Weather: The weather in November is accurately described in the first post. But I would add that being near the water in November just tends to make the air wetter and thus it feels colder. In warmer weather I might opt for Belmont Shore, but in November, Anaheim will be more comfortable.

Freeways: If you are in Belmont Shore, you will have to use I405. In Anaheim you can use I5. Traffic on I5 is usually not quite as bad as I405. And for the places you are visiting, I5 will be a bit shorter.

Price: You are likely to get more hotel for your dollar in Anaheim. There are a lot of hotels there ( because of Disneyland ) and competition drives the price down.

Welcome to California

Per MAPBLAST:
Anaheim to Valencia = 59.3 miles
Belmont Shore to Valencia = 59.7 miles
Anaheim to San Diego = 96.5 miles
Belmont Shore to San Diego = 104.9 miles
Valencia to San Diego = 155.3 miles
Anaheim to Belmont Shore = 22.1 miles

Belmont Shore in Long Beach is very nice with lots of little shops and restaurants located on 2nd Street plus the beach areas. As you leave the area heading down 2nd Street, it will turn into Westminster Blvd as soon as you cross PCH. A very short way down is Studebaker Rd, turn left which will take you to the 605 freeway North to the 91 freeway East, to the 5 freeway South if you plan to head to Anaheim where Disneyland and California Adventure are located. Sounds complicated but isn't, plus you can avoid the 405 freeway. Without traffic, it's about a 25-minute trip as I go that way at least once a week during the late morning hours after 10:00 a.m. If you don't wish to drive to the San Diego area, you can always take Amtrak out of the Anaheim station, located on the grounds of Angel Baseball Stadium. It takes you directly to downtown San Diego where you can catch a cab or bus depending on where in San Diego you're headed (zoo, Sea World, etc.). I assume Valencia is another destination because of Magic Mountain?? Personally I'd spend the night in San Diego and in Valencia as they are completely opposite from one another and if you're taking in an amusement park all day at either destination you will be tired.