Let me ask you, have you spent time with that girl you had your eyes on for three years? I mean was it just phone conversation; like distance relationship in other words? And why is getting engaged and married is the only way to be with her?
What does her rejecting several marriage proposals has to do with the advice you need? Was she rejecting those proposals to be with you?
If you are in love with and she is in love with you, then money and position and whatever wouldn't matter.
Yes, every women wants to feel secured at some point.
But I think money wise, it will work well with you.

About your age, I don't think 24 years old is considered young anymore. You are grown enough to fall in love, be loved, be responsible, grow in your career and have a family.

You can get married, live together, no need to have kids right away; if that's your concern. Then when you both are ready to have a family, then let the magic happen. ;)

But before all that, the most important thing is for you to know weither you love her or you are in love with you...

There is a big difference.

You never mentioned any of that above anyways.

In that matter, I would tell you think twice.

Best of luck!