There are already so many great and detailed answers here. I'll give some short opinions.
Take a training class or go with a gun loving friend to rent some common guns. Decide which one you like the most and shoot well. Having a gun you can personally shoot well is much more important than some feature people say you must have.
Get a flashlight on the gun or to keep with the gun. Don't put a flashlight on the gun unless you personally want to.
Get something you can easily carry all the time. The super cool full sized handgun on your desk is not as useful as the .380 in your pocket.
Spend some money. A good used gun is almost always better than a cheap new gun. Guns don't expire and it'll probably always be worth close to what you paid if you go to sell it.
Get a good holster if you're carrying. Don't be afraid to try a few and see what works. There is no right choice. It's all about what works for you.
It's all about you. Seek advice but do what feels right to you. The things that matter are how well you can shoot that gun and that you have it available if needed. You get to decide what that means to you.
Personally I carry a .357 6" revolver and a .380 bodyguard. As long as my pants have a pocket I can have the bodyguard on me.
If you have more specific questions feel free to ask but I would very highly recommend talking to someone in person.
I'm surprised no one is really talking about asexuality. Sexuality is a spectrum. It's entirely possible and perfectly fine if romantic relationships aren't as important to you as they are to other people.
I know people who spend entire nights crying and reinforcing their dogs separation anxiety because they can't find a partner. Others that are much closer to retirement than college who have never had a serious romantic partner and don't seek one.
You probably shouldn't prioritize work over personal life. You also don't have to be in relationships if you don't want to. I would recommend keeping an open mind and not getting stuck on labels. If partners and relationships aren't something you think about a lot that's ok. If not having that bothers you then you might want to seek professional help to assist in figuring out why you're avoiding relationships.
Also keep in mind that basically every country on the planet heavily encourages marriage and children so get used to skipping all those options on your taxes and benefits.