Hi Brahma,some people do use breeder pellets,and,have found them to be beneficial.If I did decide to use them,I think it would be a good idea to use them for a week or maybe two, before collecting the eggs to incubate.
Unless you've also used layers pellets with the bird's though,you wont know if it is better for your croad langshans or not.
Personally,I wouldn't ACV all the time,unless the birds are having a stressfull time,I would carry on for a week a month as normal.
Regarding tonic's and supplements,the birds should be getting all the nutrients they need from their diet.I personally do not think it does any harm for some extra's,especially when breeding to encourage good fertility and strong healthy chicks.That way,if anything is missing from their diet,or an insufficient quantity,they are being provided with it.
Most tonics/supplements are only for stress/illness etc. and not to be used daily,although seaweed,happy hen tonic are fine for general/daily use.Those are 2 that spring to my mind straight away.