Backs: 80+
Mids: 90+
Rucks: Two of top 3-4 Ruckmen
FWs: 85+
Using this as a guide for what is called a keeper, here are you potential players from last year.
Backs 80+ = 13 players
Mids 90+ = 33 players
Rucks = 4 players
Forwards 85+ = 13 players
So using your logic, you only have 63 players in total that could be called keepers and more than 50% of these are in the midfield.
Hence unless you've loaded your midfield with "keepers" you're seriously going to struggle for keepers.
Now assuming that you believe that the most amount of keepers that you can have in your starting 22 is 12. This means you need to upgrade 10 players.
Now please explain to me your trading strategy?
LTI = ?
Single trade upgrades = ?
Double trade upgrades = ?
The term long term injury changes as the year progresses, so at the start of the year it is almost anyone missing 4+ weeks, closer to the end of the year it could be someone out for 2 weeks.
Just say you leave 8 trades for LTI's. That leaves you with 12 trades to upgrade those 10 players. This would almost require you to have 8 single trades and two double trades to get your required team.
This is a very hard concept, so maybe your use of the term keeper either has to change or you need to find a way to secure more keepers in your initial squad.