I haven’t gotten my period yet XD, but I can help with a few of your questions, even though I am a few months late.
1- There’s nothing to be scared of. Puberty happens to everyone and it is a part of life. Don’t let it get you down. Every girl goes through this kind of stuff- scratch that, every person. Even boys do too. Even I get hair down there and my pits look like a jungle XD. This might mean your period is going to arrive in about a year or so.
2- This is a common horror for girls. But just know, every girl has got go through this. So even if you are stuck in this time, just talk to a female, like a teacher, but if there aren’t any present, just excuse yourself to the restroom. Speaking of, when you get symptoms like breast buds, discharge, and acne, you might want to carry around supplies and an extra pair of pants or underwear. Your first period probably won’t exude that much blood, but carry around spare underwear just in case. I recommend you carry pants when you’re familiar with your period.
3- Never feel embarrassed of your changing body. One person it is crucial to talk about to is your mom. Your mom goes through this, so just casually bring up your worries, and I bet she’ll help. Periods don’t hurt themselves, but you can get cramps, but things like ginger ale and a hot pack over your belly can help. They usually happen for a week, but it can be longer or shorter. For how many a woman has in a lifetime, it depends on when she got it, but she’ll probably have it for at least 10 years more or less. Then they reach menopause, where they stop having periods.
4- Bras for me is more of a puberty thing. For girls, when you get breast buds, it’s a sign of puberty. Bras help to keep the breast from sagging. When they grow, women and girls often need them. You only need to change clothes on your period when you leak, which is when the blood seeps through your protection.
Advice on protection- I would rather use pads, because tampons can be uncomfortable at first. Also, if you’re ready, you can use menstrual cups, which you insert down there. These collect the blood, and can be used for a long time. Also, if you’re using pads and tampons, change them every 2-3 hours, and if you don’t do this, you'll get TSS, Toxic Shock Syndrome. This is painful and can lead many other disorders.