I don't think there's a single right or wrong answer to your questions, and some of them seem more dependent on your own beliefs on the Tarot than anything else. We can give you our own opinions based on our own experiences and beliefs, but it's ultimately your choice.
I'll start with the easiest part, your fear of evil presences.
Personally, I see the Tarot as a tool like any other. When you write a story or read a book, you can get things wrong -- make grammatical mistakes, for example, or accidentally skip a word and not understand a sentence very well. That doesn't mean that you were momentarily possessed by evil spirits, just that you were distracted, inexperienced, etc., and also that as a human being you won't get everything right all of the time in your life.
If evil presences are a part of your belief system, I assume that good or neutral ones are too, and that they are as capable of communicating with you through the Tarot as well, no? Maybe it would help you to focus on that. It could also help you keep your peace of mind if you do whatever you personally believe will protect you, whether that's saying a prayer or keeping an amulet around.
I should also note that you don't have to use the Tarot for spiritual purposes like divination. You can use it as a tool to learn more about yourself or simply as something new to learn about, by doing more "mundane" readings or using the cards as a starting point for reflection. There are also things like storytelling spreads. How you use the cards is really up to you.
Next: your fear that you might let go of your free will and get stuck doing something based on an erroneous reading. That's completely understandable. You can do a variety of different things with the cards, not just read about your future. When I do that, I don't really see the cards as telling me what WILL happen, but what is most likely to happen based on the present. I find it helpful to add to my readings something about different possible outcomes based on different courses of action, as well as asking for advice on how to change a possible outcome. All of this depends on how you think of the cards and what you do with them. There's no right or wrong answer because it's a personal thing.
Finally, your concern that this will be a negative experience for you because you're a very sensitive person. My usual rule is to not read about things I don't want to get answer for or if one of the possible answers is something I wouldn't want to hear. That might help you. You're also free to do more lighthearted readings that won't shake you up very much emotionally. Lots of people feel like their readings with certain decks also sound rather blunt or harsh. Maybe you could take that into account when choosing your deck(s); not what others think of them, but how the artwork and imagery feels to you, and what you believe would be best for you right now.
If you're very susceptible to things or are afraid of becoming anxious or scared over something, maybe you should reconsider. In my opinion, there's nothing particularly scary about the Tarot. However, if it scares YOU, then maybe it's not your cup of tea.
Based on your post, maybe you should wait until you're more comfortable, but it's a short post on a forum and it doesn't make me an authority on your life. If your fears are coming across as being stronger than they really are and you're more comfortable with it than you sound, get into it slowly. Work at your own pace, set your own boundaries and decide whether to stick with them (stop if you're feeling seriously uncomfortable or unwell), and so what feels right to you. It could also help to find someone reputable in your area who can give you feedback, find an open-minded friend who can snap you out of it if you start getting too caught up in it, or, if none of these are possible, you can always post here if you're afraid of something and we'll tell you our own experiences and help you out.
There's so much within the world of Tarot that it's hard to tell whether it's for you or not. I don't want to lie and pretend that any of us knows what's best for your own circumstances.
EDIT: Another idea, it might be easier for you to decide if you learn about the Tarot as much as possible beforehand. Read a few threads here in this forum, for example. It's probably less daunting to figure out whether it's for you if you know a bit about what it entails.