About the trainer. Its not really proven that it is necessary to have a trainer above level 4. The differences seem to be very little. But if you can afford you can get yourself a level 5 trainer. but at least level 4.
Here I'm not agree with you, my friend, because if you want to have a NT/U21 player, you need at least a lvl 5 coach. Because, the difference between a lvl 4 and lvl 6 training is significant for a player for u21 squad, you earn few skill up's,in few seasons, and this is very important for a u21 prospect. Generally, I think, the lvl 6 or 7 is the best for such prospects, but they are situations when some teams con afford big salaries and money to buy such coaches, and in this situations, the optimal solution is to buy a lvl 5 coach, but if you want to have a marvelous player in u21 team, you must buy a lvl 6-7 trainer, and I say you this basing on my own experienced, because I had a lot of trainer of different lvl's, and my conclusion is this :-)