I do software dev in LA, and have worked with my share of project managers.

You'll be working frequently with engineers. It helps if you come across more as a peer, rather than part of a ladder. Most tech people hate the idea of the corporate ladder. They believe in flat structures and meritocracy. Not that that's reality, mind you. But it's the ideal. This is deeply ingrained in hacker culture, going back to the '60s, '70s, and '80s. The disdain for "suits" is real.

You'll need the support of devs to get your ideas into fruition, and it really helps if they feel they can come to you and just have a casual conversation rather than speaking to an authority figure.

That said, wearing a pair of slacks and a tucked in shirt will be fine. The developers know you have multiple roles to fulfill. Be careful if you're in Santa Monica/Venice. The people outside your office are going to dress very decent. Embarrassingly decent, at times. The temptation to match them will be real. Don't get too caught up in the peacocking and overdo it.