Udinpetot

It will be better to follow others of your local office and guess an estimated timeline for your N-400.  N-400 is getting more push recently, so your waiting time will be less and compare to other immigration stages, N-400 is more straight forward and a lot less burden of prove, since they now know everything about you, since you already provided a lot. 

You would think wouldn’t you? But since I have to upload my divorce decree from my first marriage and my marriage certificate  (both of which they already have from my green card application) I wouldn’t be so sure.
 
But I agree that your tax returns are a good option. 

Marriage certificate?

You bear the burden of proving your eligibility for citizenship. Go through each of the eligibility requirements and consider what documents you will need to establish eligibility on all grounds.