I am part of this generation that some people are calling the "hopeless" generation. The problem with some of the things that have been mentioned above like cars for example: so many things have changed in the 12 years from when I first bought my car at 15. It was a 1966 Mustang 289. My dad and I stripped down the vehicle in virtually no time and put it back together with ease. The reason being everything in those vehicles were mechanical, not electric or computerized. I now have 7 year old pickup with 130,000 miles on it that when I open the hood about the only thing I can change with my limited amount of knowledge is the headlights. I do agree for the most part that in theory it is relatively easy to become a millionaire, the problem is that a million bucks doesn't do what it used to. In the 6 years I have been out of college, I am living in my second house driving the pickup that I purchased after my one from high school was totaled, the wife is driving the same car that she has had since 2005. We sold our first house for a 50K profit (on a 100K purchase price) and put most of that money into another house to pay down and to where I only had about a 65% LTV after purchase. I am an accountant working on my CPA license, wife is a school teacher, and I consider my self "with it" financially speaking, but it is still difficult to get ahead as a young person. That is why you see more "millennial" living with their parents than at any other time in history.
Congrats on the profit you made from your first home. Now I can't give recommendations over a forum like this because were it to be discovered, I'd get heavily fined.
When it comes to cars, I tell everyone the same thing. Never ever have a car payment, period. Pay cash, but a clunker if you must, sell it, and put that money with other money you saved and buy a nicer car. If you want a new car, start a car fund and add the equivalent of a car payment to that savings every month. Eventually you can walk into that dealership and tell them what you want and just give them a check. There isn't a better feeling in the world, unless you are paying off your house.
Pay off your house. You want to be a millionaire, pay off your house and live mortgage free. You would be surprised what you can do when you have an extra 2000 per month to put away for retirement.
Max out all Tax-free growth instruments. 529 plans, Roth IRA, Whole Life Insurance,
Get at lease a 6 month reserve of money and don't touch it except for emergencies
Stick with your job. The last statistics I saw was that most employees stay with a job on average for 5 years. If you want to make real money you got to stay longer than that, especially if you are in a strong company. I have a good friend that went to works for a warehouse store pushing carts in 1987. Today he is still with that company only now he is a regional manager. He is also a millionaire. My dad is retired with a very nice retirement because he put in 20 years in the Army as an NCO, and then 20 years at the Post office. Government folks call this double dipping, because he gets 2 pension checks per month.
Make sure your wife is on board with these things, you can't get it done unless she is 100% with you.
Budget in fun, when you are putting this together don't be afraid to budget in fun. You don't have to take a vacation to the French Riviera, but you can budget to have a little fun it takes the edge off of sticking with a budget.
Finally, and most important, if you are living off of one income, make sure you have adequate disability insurance. If you are living off of two incomes, learn to live off of one and put the other into savings. But still have adequate disability insurance. You are far more likely to get injured an unable to work than you are to die.
That is my soap box spiel I give to young people.