Best way to have a 7 star team

[Toxcatl]

What is the best way to build a 7 star team of players?
1) Buy 5 star 18 years old fast trainers and use green packs ?
2) Buy 5 star players that almost have 6 stars but might be slightly older ?


From people with experience what is the best approach to the game to reach high star levels ?

Buy 3 FT every season, train them up to 120% asap, then train FTs from previous seasons, then save greens for the next season. Repeat.