>>36031192I usually go for at least Lv60 when I'm fighting Steven, but your team looks pretty solid (I tend to run slightly weird/bad mons) so you may be able to win with lower levels. Having some general strategy for taking down each of his team members definitely helps.
Here's my Sun team. I've just finished Akala and I'm about to head to Aether Paradise for the first time. Torracat is probably going to get ditched for Turtonator when I can catch one - Fire/Dragon is a pretty cool typing and I've already used Incineroar twice before.