You can make any game with unity as long as you have enough skill, time and money. It won’t limit you into any genre because you can just write your own C# code
Depends entirely on the type of game and the scope you are thinking of. There is no real answer for such question. If you are doing everything on your own, keep in mind to be busy for a few years. For example, I’m working on my own with my project and I’ve been working on it for about 2 years now. From scratch, zero knowledge.
The only limit that unity gives you in the free downloadable version are the maximum annual revenue of 100 000 dollar and the restriction of the Pro only features (you can find a comparison list somewhere on the site). There are some other legal things I suppose, but those are the major restrictions AFAIK
Again, depends on your game scope, your current skill, how fast you can learn things etc etc. The question is too vague for a decent answer. The hardest thing for a beginner is to learn programming though. This is one of the few things you have to be really comfortable with before you can DO something with it. Anyone can download photoshop or blender and do some painting/modeling work. Making it look decent is another story though.
Like I mentioned before, you need to learn programming before you can even consider putting a game together. You could be the best modeler, texturer, game designer, concept artist ,level designer, sound engineer, project manager, play tester… But without programming there won’t be a game if you work on your own. Start with learning the basic syntax. Personally I recommend to go and learn C#, look up the tutorials found on the unity site, maybe Burgzergarcade’s tutorial series. Make sure you get familliar with programming.
After all, If you expected to make a small horror game within a week without any knowledge in advance, and don’t want to spend much more time on that, you’d be better off doing something else than game development. If you are willing to dedicate a lot of your time, dive straight in man
Just a warning that the learning curve can be a steep one and quite overwhelming in the beginning