Hangling training is critical. Wouldn't advise to let your Assistant to take care of if. Training has nothing to do with the short term success of your tactic. Whether you train or not, it is going to have a very little impact of how your team exesutes its tactic for that season, aside from match training of course. General Training and Individual training is for the long term development of your players. You wan't your players to reach their full potential and also fit your tactical roles right? You Assist is going to do a poor job at that. It is not something you have to adjust every day, and isn't time consuming.
As for OIs, ya you can have your Assist set that, but again, he may do a poor job at it. You have to make sure that he has a high tactical knowledge and his playing style fits the style of your tactic.
