Unless you have operating room clean track and wheel sets, the relays will experience chatter. You can add the capacitor(s) as you've suggested to avoid this condition. And as you have stated, this is easier with DC relay coils.
I would suggest that the cheap relay modules from eBay are SO CHEAP as to make them a compelling purchase. You can afford extras. In my experience, they work as advertised. They also use opto-isolators on the inputs that provide additional protection for the relays. And there is a back EMF diode across the coils that prevent voltage spikes. I doubt that you could do better than that.
