Hi C.,
Good for you for taking charge of how you appear!
First, I recommend you decide what is the most important things in first impressions that you want to make, write it down so you keep it clear to yourself, and then how much time and money you will budget to get that. Hair can have surprise costs in both time adn money if you don't make some choices about it up front.
Here's what I did, if it helps, great. If it doesn't, then never mind.
I was frustrated when I was young, I was in a man's technical world (military) went gray at 26, and was grateful since I was in a technical job, low credibilty because I was young and female, and looked like I was 16 otherwise. So I left it go gray naturally, cut it to be professional and go well with the graying process. that was a brilliant decision and it paid in promotions and credibilty with first impressions.
At 32, I moved to consulting, and for the interviews and through that part of my career, I rinsed my hair strawberry blond (the gray came through as a lighter color, very nice), cut it in a short, professional cut, and I got much more crediblity that way at that age because I no longer looked 16, and the first impressions of hair appearance as energetic, simple and neat, were critical as a consultant.
My sister had similar fate in the technical world, but because she was blond and pretty, she suffered from people talking in single sylables and simple sentances. So when she went gray, it was MUCH better. Now she gets professioally done highlights in her hair and it's a browner color with some gray.
I don't color my hair anymore, just keep it mid-length and simple and professional, I am 53, get it styled and cut once every 6 weeks or so, use great quality shampoo and conditioners, and the natural differences in color plus good care, make my hair exactly how I like it; simple and framing my face without distractions so people see me, not my hair. I have some white in it now, and the cut is critical to show it off well and elegantly.
Best to you, and if you have detailed questions on what cuts I got, shapes, how the hair highlights itself depending on how you fix it, feel free to email me.
You'll do great! Just keep that list of goals in front of you and it will be easy to focus in and get those effects.
M.