That's funny. If I were to give advice to anyone, even a brand new player, it would be the opposite of both the older players and the hoarding strategies.
I've always been a fan of training, and focused on developing my own talent. I think it's so much more fun to play the game and build that connection with my players as they slowly get better and become what I want them to be.
For players and for team building, I'd say always aim at least one step ahead of where you are. If you're in D3, then don't just build a team for D3, but make sure your players are good enough for D2 as well. If you're in D2, don't just push to win it once and then struggle in D1 - build a team of D1 ready players. That doesn't mean put together an 800k salary roster in D2 - but that each player has a role. Probably 3 of your D2 starters should be D1 ready, and the other 2 should be capable D1 backups. You fill in the extra gaps in your roster when you move up and can afford it, the promotion prize money helps.
(As a general rule, your stars in D3 should be at least role players in D2, and should be at least backup material for D1. There's no point in investing in a superstar offensive player in D3 who only has say 9-10 OD, when they're not going to be as great offensively in higher divisions, and defensively they're a huge liability).
More importantly though, you should learn to manage enthusiasm and game shape. You'll be so far ahead of so many managers if you get those two things under control.
For the finances/hoarding advice, I'll be honest - there's only one time in my entire BB history that I even hit 10M, and that was around mid-2018 when I was undergoing a serious training regime getting Omu and Whitney ready. Apart from that exception, I don't think I've ever hit 5M. My finances tend to fluctuate between 1-2M mostly. The important thing here is to manage your weekly economy. If you're making profit each week, happy days. Managing enth and GS helps so much here, because you can then stay competitive with a cheaper roster if done right.
25M is unnecessary. I built my team as I went, finding what I needed when I needed it, never having massive hoards if money. I just had a plan of what I needed in the end, went towards that. If you're making a profit each week, you can make things work, and if not, then learn to trim down and be efficient with what you have.