If you want to live in the world of Touhou:
You will just get immediately eaten by youkai. Outside world humans that get spirited away into Gensokyo aren't protected; youkai aren't allowed to eat native humans from the village, but outsiders are fair game. That is, unless the outsider can make it to the human village, where they can become protected once they've integrated with the natives. Even then, there are some aggressive youkai that break the rules and attack the village anyway. But it's not all bad. Some youkai are nice and don't eat humans, I would assume that's the case with Alice Margatroid. You could probably even learn magic and become a spell card user, so you can venture out of the village and defend yourself from creatures such as youkai and fairies. But that would be very difficult and literally takes a lifetime of work to become even a decent danmaku user - Marisa Kirisame is the only human spell card user we know of who wasn't just born with or granted powers.
Reimu Hakurei: Gets her powers from being a Hakurei shrine maiden, only blood members of the Hakurei clan can use the Yin-Yangs. Though despite being born with her powers, she does sometimes have to train to gain access to or strengthen certain powers.
Sakuya Izayoi: Her time manipulation and danmaku powers are of mysterious origin, though they might've been bestowed by Remilia Scarlet after becoming her maid. It's theorized that Sakuya was formerly a vampire hunter with no magic and only knife skills, but Remilia mopped the floor with her, after which she offered to spare her life on the condition that Sakuya becomes her servant.
Youmu Konpaku: She's only half human. Supposedly most of her powers come from being half phantom, and most of her danmaku is created using her swords, which are said to be forged by youkai.
Sanae Kochiya: As a human shrine maiden, not only may she have inherited her powers, but she's partially a goddess very far back in her bloodline, and it's possible that her powers were strengthened by Kanako and Suwako when they first came to Gensokyo.
That being said, Marisa isn't like any of them. She was formerly a mundane human with no magic or special properties whatsoever, before she began training herself and learning magic. Supposedly, magic is much harder for humans to grasp than youkai, as most youkai just naturally have their powers (though some do study magic to become stronger than the average youkai). Despite having worked hard most of her life to become a talented magician, Marisa only barely rivals Reimu, whom doesn't even need to train to be slightly stronger than Marisa. Suffice to say, if you get spirited away into Gensokyo and want to learn magic in order to defend yourself from hostile entities like phantoms, fairies, and especially youkai, you're gonna have a hard time. And I somewhat doubt you can ask Marisa for help, because stopping to help some freeloader would slow her down from her research and training.
Another possibility is the kappa. They're skilled engineers; although they already have certain powers due to being a type of youkai, most of their power comes from their machines, and much of their danmaku is enhanced by or even produced by their weaponry and other equipment. And the kappa are a particular type of youkai that are actually nice to humans, albeit a bit shy. I'm still not sure if they would be willing to share anything with you, unless you get real friendly with them I guess. Still, the kappa reside mostly at the Genbu Ravine, which is somewhat far from the village and near some of the most dangerous places in Gensokyo, you would have to pass by the Misty Lake, Forest of Magic, Great Youkai Forest, and the ravine itself is at the foot of the Youkai Mountain.
Or you could just not gain any power at all, and just stay in the relative safety of the human village. It would be a peaceful but maybe boring life. After all, you would be giving up certain things you have in real life, such as the computer you're using to read this - the human village is unfamiliar with modern technology, it was isolated from the outside world centuries ago, so it's like a snapshot of ancient Japan.
Still, I suggested this because it's a world with many possibilities. If you're very lucky, you could gain a foothold in this world if you manage to become a spell card user. If you get strong enough, you could maybe even take part in incidents, or even become an incident resolver. Even if you don't gain any supernatural powers, there's friends to make here. And if all else fails, and you find this dangerous world too risky to live in, you can have Reimu guide you back through the Hakurei Barrier into the outside world. That would essentially mean abandoning this fantastical world to return to real life.
