I'm sure the short answer to this is something along the lines of "could go either way".
Considering your last sentence, you sound like you might got a problem with an overactive imagination and intrusive thoughts. Those tend to be a problem when making tulpas in the first place and well, if things tend to turn out to be something that is a problem to you in your imagination, it could happen again. People with some mental disorders apparently have made tulpas in the past, but this far it seems like it helps some and hinders others. I don't think there is one definite answer here, as it's mostly up to how you handle the situation. So I guess a fair warning is in point as we possibly can't know what would happen, but a fair warning might very well be given to every single person interested in tulpas.
From my personal experience, tulpas tend to help with a lot. Feels like they can make you understand so much about yourself and become a more balanced person in the end, which is a pretty huge plus I gotta say, something you probably are after as well. But for you to create a tulpa, you seem like you would have to go fight your other problems on your own first. Things "turning out like your nightmares" when you haven't intended them to is an issue that to me, would most likely affect making tuppers. First and foremost you would need to understand that you are safe in your mind and that you have the power to control everything by just making it happen. Creating such a, uh, peaceful mental environment would also be a good first step to overcome your own issues, as there would at least be one place in the world where nothing would hurt you. And such peace and calm is a pretty good starting point before you go adding tuppers.
Making a tulpa might force you to learn that before you really get anywhere. But I'd say it is a skill you need to learn sooner or later, but when you want to do so, up to you I guess. Up to you if you even want to make a tulpa, knowing that there might be some risks. But obviously, just like any other person, a tulpa could help you with much and the process itself can be pretty helpful.
