no, you can have nikkah and walima together. nikkah is only the actual marriage part. if it's an event (party/dinner, therefore announced), that constitutes walima too. it sounds like they had a one day function. lots of marriages are and were done like this - my parents, some of my cousins, my own.
I didn't know that. It sounds more affordable, though
And you could have one really nice function instead of 3-4 different parties
Me likey