is it ok to?

fellas is it gay to smile?

I mean doesn't it depend on the situation/location? I used to walk to work and it was common to get a 'good morning' from people of any gender, though more often they were older people. And from that interaction I never assumed their sexuality. I get queues from other things, but that act alone doesn't indicate sexual interest. Just avoid too much eye contact/lingering smiles like you would with a cashier or stranger in general.

If you notice the person has head-phones on, is looking down at the ground, and has their hands in their pockets, respect that they want to be alone in their minds. If the person seems more open to the world around them, why not?

I think if your intentions are purely friendly and not sexual, they will catch your vibe. If your intentions are otherwise, they'll also take the hint also. I'd recommend for the latter interactions to be avoided in situations where people have the expectation of not being ogled or targeted, when they're just going about their day. For example, walking to work. Shopping, etc. Until you have a signal of some consent for more. For example, if you see the person often and have an "in" as a result. Feed a relationship with the food it's ready for. Like watering plants what they need: too much and the roots rot. e.g. when I got a 'good morning' or 'hello' it was fine. When I got a "what's your name" from a rando I was passing on the path, like... um... please leave me alone.

Yes, it's always ok to be friendly

Of course it's fine. Say hello with a smile, pay a genuine compliment, then MOVE ON.

Just drop the smile and say hello to strangers and you won't look as strange.

It's fine to say hello to strangers. People sometimes say hi to me when I'm walking about.

Yes. It's OK. And since you are gay, you shouldn't be concerned what anyone thinks about that.