What is the current state of the United States Nuclear arsenal?

I just wanted to get some opinions from those that know about nuclear weapons or are interested in the subject, what they think is the current state of the United States nuclear arsenal. It seems to me a lot of stuff is old and outdated and we are not trying to modernize as fast as I think we should. It seems like I constantly see where we are retiring this bomb or that bomb and that we are no longer making plutonium pits and it is no longer feasible to try to update some of our missiles because they are so old we no longer even have the blueprints! It just seems to me with all that is happening in the world that now is the time to update, upgrade and expand our nuclear arsenal and that if keep kicking the can down the road we could get caught with our pants around our ankles. Russia seems to be expanding its nuclear arsenal along with China and that China may have nuclear parity with the United States in a decade or so. North Korea is expected to keep expanding their arsenal and keep working on missile systems able to hit the mainland United States (I do know they already have at least one ICBM that can supposedly hit Washington DC). Any thoughts?