You are right - Everything can be improved, otherwise there are no opportunities to grow.
Not different if you'll be the coach of u-21 or I'll be at the head of national team. Indonesian players are weak. It's necessary to grow talanted yourth with activity and to use one slot for training. Many managers should be involved in that work.
Another point. Nobody can help you with tactics and game plan, because nobody knows skills of the indonesian players. Why? The strong team will win you in any case. With equal team there is one principle thing - tactics. You set tactics yourself and keep it closed from the opponents. So you can open skills of u-21 players for more discuss at the forum.