So the accusative pronoun only precedes the verb is the subject/nominative pronoun is stated?
Generally, yes. It sounds more natural that way. Although sometimes if we want to stress the object of the sentence we put it at the beginning. E.g. "Kochamy was" - We love you. "Was kochamy" - [It is] you [that] we love. It's a bit unusual but not unheard of. Usually in speech, though, if we want to stress the object we just stress it with intonation and use the usual word order.
Are there any charts that show how the word changes in the different cases?
I can't recommend anything specific right now, but there are a lot of useful resources here: https://forum.duolingo.com/comment/16296174
As for specific words, the English Wiktionary should have almost all the words we teach and I've seen it being wrong literally two times, so it seems rather safe.
"Was" is for singular or plural "you"? What means this in German? It' s a bit confusing, "cię" means also you...
'was' is Accusative of plural 'you'.
It means "what" in German.
"cię" is Accusative of singular 'you'. It's the English that's confusing ;)
It does not sound like "was" It's very unclear, kind of muffled even when slowed down. Sounds like "do"