Sell or Train? PLEASE HELP!

Steve Goodyear Add Shortcut
17 y/o (R3, D5) | 16,911 CSR | $4,557 p.w. | 199cm | 124kg | England
Left handed, left footed, in decent form Stable.
An aggressive player with controlled discipline, average leadership, and non-existent experience.
Energy:
Energised
75%
Stamina: Average Handling: Satisfactory
Attack: Decent Defense: Admirable
Technique: Decent Strength: Decent
Jumping: Satisfactory Speed: Horrible
Agility: Horrible Kicking: Despicable

Just promoted this guy from my academy, his stats and untrainables aren't too bad but his CSR is really low. Will this affect his performance? Along with other players I'm training, I can probable bump him up 400-500CSR per week.
My current locks are:

4. Jake Mutch Add Shortcut (Injured)
21 y/o (R2, D1) | 24,852 CSR (+202) | $6,080 p.w. | 201cm | 108kg | Ireland
Right handed, left footed, in admirable form Stable.
A collected player with collected discipline, average leadership, and limited experience.
Energy:
Supercharged
91%
Stamina: Admirable Handling: Decent
Attack: Decent Defense: Admirable
Technique: Reputable Strength: Decent
Jumping: Decent Speed: Moderate
Agility: Moderate Kicking: Horrible
5. Penisimani Hufanga Add Shortcut
20 y/o (R11, D6) | 31,440 CSR (+249) | $6,879 p.w. | 196cm | 103kg | Australia
Right handed, right footed, in satisfactory form Stable.
A timid player with reckless discipline, non-existent leadership, and horrible experience.
Energy:
Perfect
101%
Stamina: Impressive Handling: Satisfactory
Attack: Moderate Defense: Reputable
Technique: Impressive Strength: Decent
Jumping: Reputable Speed: Admirable
Agility: Limited Kicking: Horrible

i would make goodyear a lock and hufanga a flanker due to having 10 speed.