To be honest, a lot of teams expanded trough the creation of one star, a little like Lebron James allowed Cleveland to reach the Finals. You'll say that now he is gone, they are back to zero, but imagine that here, it's possible to negociate a good transition.
The reason that star players are so important in the NBA is that there is a ceiling on the amount individual players can be paid. If there was no cap and Lebron received his true value, he would command over half his teams' salary and they would probably be pretty average without the massive luxury tax. Also Lebron in this game would have a 600k salary.
Your first star will allow you to win D5 and D4 just by getting himself, then after that he will save you in D3 and you can start to think about the transition. Back in my days, a future French NT allowed me to go from D4 to D2, then make some money to get a nice team. With his money, I bought the current biggest salary of my team who ship me to three seasons in the D1 and could get me back there again this season.
You first made D2 in season 9. Stadiums are bigger now and the transfer market is cheaper. I do not doubt this is a viable way to build a team, but I am still not convinced it is the fastest (optimal) way. There are two main reasons:
First, training and money really ARE interchangeable because of the transfer market. There are certain trainees that will be undervalued relative to your needs, and certain trainees will be overvalued. Train and sell the overvalued ones, and then buy and train the undervalued ones. The transaction costs are low. Put another way, it is unlikely that the most profitable trainee will also be the trainee who is best for you, and at some point it will almost always be possible to swap the two while making a profit. Or better yet, buy oldish guys who depreciate less with the cash and just keep making money selling trainees.
Second, in my admittedly limited experience, the more balanced a team is the more likely it is to punch above its salary weight. It makes sense because of the exponential nature of skill cost: a 10k increase in salary will buy a lot more skills on a 15k player than it will on a 25k player. Now of course there are viable tactics and strategies that make certain players more important that can be quite effective, and I'm not saying your top 8 players should always have the same salary. But I think that especially for newer managers, a more balanced approach will win more games for the same salary most of the time.