One more factor to consider: if you do file N400, current estimates (depending on field office), you will be looking at around ~7-9 months. What if you get your combo interview in May? Upon approval, the interviewing officer will take your green card away. Now you can't travel until you get a U.S. passport, which could take another month or two (if not more, since you have to get all the documents proving your citizenship first). You will miss your sibling's wedding because you will be stuck in the US.
How likely is for this to happen right before your travel? I reckon about as likely as getting the i-751 denied while abroad.