Hey there!
I believe that, yes, most salons can do that sort of dye in one sitting. I think it would be especially beneficial for you to check out some places in your area, and find out if anyone can put you at ease. Many professionals will have done lots of different kinds of dye jobs, and many of them will be able to give you advice, and a professional opinion about what you’re looking for.
I also find it helpful to look at pictures of what I want, in order to solidify the idea in my head about whether I like what I’m getting or not.
And remember- hair will grow out. If you hate it, you can either dye it again (though hair is not infinitely dye-able and you may want to take an easier route for your first step, such as trying a colour that is darker than the rest, but still light enough that it would come out easily) or let it grow out and then chop off what you don’t like.