Is Oct or Nov good time to visit Thailand? Me and my friend want to go for 3 weeks, but these are only months?

we can get the time off. We are wanting to have first 2 weeks at beach resort and last week in city of bangkok. Will the weather be good for beach resort, will it be nice to swim in sea and get suntan etc, where is best to go for beach resort and what dates would be best in Oct - Nov for 3 weeks. Thanks