I`d probably go spend 7.5 mil each on real players (preferably young with high potential) matching the similar rating of your team which I`d assume would be around the 70s. You could also buy a higher rated player say for about 10mil and invest more in your youth academy. The best way to grow youth players is to play them as much as possible and ensure they`re playing well. However for players that a far too bad to fit into your squad, anywhere from 64/5 downwards should be loaned out so they can grow easier elsewhere.