Will an Apple Watch Series 4 work with my iPhone 6

Maybe.

Apple no longer sells the series 4, so anything you find brand new, is likely old stock.

If it is old stock and had never been updated, so is still running watchOS 5, then it can pair with an iPhone 6.

However, if it has been updated to watchOS 6 or later, it will not work.

will I need to buy a new watch charger fir my new series watch if I have my old series 4 watch charger?

bernadettefromwashington wrote:

will I need to buy a new watch charger fir my new series watch if I have my old series 4 watch charger?

No. You can use the same charger.