Naming ceremonies usually last about 20 minutes they can either be lead by the parents or by a trained 'celebrant'. During the ceremony, parents state their love and commitment to their child and declare hopes for their future. They can choose to do a poetry reading or a favourite piece of prose, with music playing in the background.
Rather than godparents, whose traditional role is to help guide the child in a Christian life, 'supporting adults' or 'mentors' (who may be friends or family) just need to say that they will be there for the child as he or she grows up and throughout their life in whatever way is needed.
Presumably some certificate is provided, followed by some photos and a jolly good knees up. I would imagine that the dress code is as per any formal family party or gathering, but not too formal, unless you are a mentor. If in doubt, ask the parents.