it says status ongoing with 0 volumes, does that mean the oneshot got picked up for serialization?

Highly likely, it is usually like that if the oneshot if complete but there is another tag that says ongoing on MU.

There's already 3 or 4 chapters out. The one-shot was released quite a while ago. I believe some time in 2011 or the beginning of this year.

cool thx for the info

Should I avoid the oneshot?
Nisekoi (oneshot) spoiled the whole story 😮

The oneshot and the manga itself have a different setup so your safe to go for the oneshot since the manga itself does an original attempt, same main characters but different name i think, new characters in the serialization. Depends on what you want to do although, i personally liked both, but have read comments that some liked the oneshot but others the serialization chapter more.

Read the oneshot, its safe. And besides the series is based from the oneshot. A refined version since its now weekly 🙂