When should I upgrade facilities?

Should I upgrade facilities regularly by selling up and working back up or should I build a strong team first and upgrade when the team is worth millions?

Better to spend your cash to get constantly better and younger players, untill you have about 20M to spare so you can get LTF(Black). Sometimes even STF(grey) works but it's not a clear option... depends on your playing style I would say, how active on trading are you and how fast you want to progress...

Youve got a STG at the moment so i wouldnt be concerned about buying and selling players as your training ground will not progress them and they may drop in value if you spend big (most likely will) I would focus on upgrading all players and league success (revenue through tickets) so stadium upgrades for the time being and once you've built up enough cash to get training ground upgrades move from there. Keep creating youth talents and make sure your trainers have 20 in training youth prospects you may create a hidden gem who could potentially be sold for millions

UPDATE

I have now got an extended training ground, 6m squad value and 4m balance, with a high squad turnover which is bad for competitiveness but good for finances and building up the facilities and the team in general.

Would it be wise to upgrade now or should I keep trading or should I spend the 4m on first team players and trade less? I like developing players and that doesn't seem wise until facilities are upgraded from. Grounds to facilities.

Trading if you want to progress fast and have the time for it… or you’ll never get to wctf or it will take 10x as long