answering your questions as best I can (I'm a straight male too) in order:

1. if he/him seems right to you, then your pronouns are he/him. if other pronouns seem right to you, then your pronouns are those pronouns. pronouns don't have to match up with your gender or presentation, go with whatever you vibe with
2. when meeting new people, I give my name and pronouns. "hi, my name is salarua and my pronouns are he/him." of course, it's nice to give your pronouns when asked, but other than that it's up to you
3. just including your pronouns in your profile is good. some people put them in their nicks, some in their bio or about me. if you have a Mastodon, Akkoma, Misskey, or Firefish account you can put your pronouns in your custom fields
4. you can try and figure out other people's pronouns from how other people refer to them. many people will also give their pronouns if you introduce yourself with your pronouns. it's not a faux pas to not know someone's pronouns beforehand, although I admit I don't know a non-awkward way to ask someone their pronouns
5. a good bet is to refer to people whose pronouns you don't know as they/them. if you mispronoun someone by mistake, quietly correct yourself and continue with whatever you're saying. "so after arriving at the office, he- sorry, they went to go see their supervisor about the presentation..." as long as it's not done out of malice, people don't mind being mispronouned if you acknowledge the slip-up and move on
6. I haven't met anyone irl with neopronouns either. presumably people with neopronouns would go by them if they were among people they felt safe with. unfortunately most of the world isn't safe :(

First off, thanks for asking and wanting to be more inclusive! :)

For your pronouns, you decide. If you typically go by "he/him" you can keep doing that, it's up to you.

Depending on the setting, people around you might all introduce themselves with their prefered pronouns, you can introduce yourself with your pronouns if you wish to whenever though.

Similar to how you might tell people a different name you prefer to go by. So if your given name was Nicholas but you prefere to go by "Nick," you might introduce yourself like, "Nice to meet you, I'm Nicholas, but just call me Nick." likewise, you can say something like, "Nice to meet you, I'm Nick, He/Him"

Online, it's fairly common now to have your pronouns in your profile or bio. Again, it's up to you if you want to put them in your bio or not. Some sites have actual places in the sign up screen or profile page to place your pronouns, it depends on the site/software.

It's rare for people to get offended IRL if you unintentionally mis-gender them. Most people will correct you politely in the same way they might if you called them by an incorrect name. So if you said, "Hey Nicholas, how are your classes going this semester?" they might say, "Oh, you can just call me Nick. Classes are going well so far, how about yours?"

Often people that know them will correct you politely too if you don't know and used the wrong pronouns. I've had it happen a few times over the years and everybody has always been very polite about it. I just quickly say, "oh sorry, my bad." and then just make sure to remember their pronouns going forward.

I personally have some family and friends that use they/them vs she/her or he/him. It's a thing for sure, we all support them and their pronouns. It's not very tough to get used to, and as long as you correct yourself if you make a mistake, nobody will be hurt. It's fundamentally about loving them and being inclusive and supportive.

Your pronouns are the ones you want to be referred to as, its that simple. So yeah, he/him if thats what you want people to use.

As for gender neutral pronouns, I just use them by default for everyone, especially on the internet when you have no idea who you are talking to as it is all anonymous (unless they have specified their pronouns in their bio/profile of course)

But overall you just get in the habit of using "they/them" unless explicitly you know their gender.

Once you get in the habit of it, it becomes more natural and you stop thinking about it.

Thats pretty much all there is to it, its quite simple and people who moan and complain about gender stuff are either:

1. Lazy, and dont want to put in the 1% of effort it requires to not be shitty

2. Really just bigoted but cant admit it out loud, so they complain about such things as a dog whistle to other bigots

3. Are extremely misinformed about what is expected of them. They seriously think the real world is out to get them, and that if they misgender someone they'll get attacked for it (in reality maybe 1 person coughs uncomfortably and they get informed as an aside awkwardly). Non zero chance these folks also think vaccines cause autism and 5G causes cancer.

Don't ask for other people to identify you, please.

I find the use of the term guys exclusive.