Trying to come up with a formidable strategy, so here is my limited view:
1) coaches are important, but not substantial--well not in low divisions anyway. 2,000 price coaches are sufficient to win a conference. However, since money is not "tight" you can splurge on mid-level guys. However, this may be at the expense of the long-term stadium size.
2) let someone else train your "studs". Buy low potential players with high skill set. Sell your high potential players for early profit. Make sure you get the money you deserve though. After all a MVP is a MVP. But a 26 year old MVP is as good as as a 26 year old 6th man with the same stats...keep that in mind.
3) Draft - make sure you scout well. You will want the best possible players. To either train or sell, preferably one train in season 2. 2 scouts per week should be fine.
4) building a stadium early will have a better payback period. Therefore, get the stadium size up early. Consider lowering prices and look at the top stadiums of top teams in the league above you as a reference. That is what you want as you will fill those seats come playoff time--and towards mid-year the next year.
5) level 5 teams are scrubs. The only challenge is to beat the other non-bots in the conference. Strategy for this should be to get gameshape and enthusiasm up for the playoffs. Buy fundamentally strong players at low market prices. Do not buy anyone over 200K unless you are certain they can be surrounded by good role players. Wait until the end of the season to buy anyone large...if you have the cash.
6) Use the transfer wire to build around either a "short" 18-20 year old training squad or "tall" 18-20 squad. Try to pick players from your country. Try to pick players with similar skills that will mesh well in training. In your first season, your training will be mild. Suggested 6-8 player training OR 2-3 position training. This is the only time where this training is optimal because your 18 year old trainers can also be your very strong starters.
7) Pick "starters" opposite of your trainers. These guys will be your "star" players. Suggest 5000-7500 price range.
8) Play TIE whenever possible.
9) Check your opponents game stats. If they play well vs inside teams, score outside. If they score well inside consider a 2-3 zone. If they completely suck push the ball or run a fast set wherever they are vunerable. Using the right strategy will seamingly get you 20-30 point wins.
10) do not be afraid to trade players. But keep anyone around that fits your training OR can "start" opposed your trainees. They will earn you good cash by staying on your team.
11) buy/sell players regularly. Keep in mind though that you want most of your team to be from your home country. Overall, I'd suggest picking players with stats that can allow your team to switch strategies by the game. It will keep any non-bots from thinking they have a chance against beating your squad...to the point where you may win the league without a decent challenge.
12) If you can get your hands on an NT type player, feel free to go that route. Keep in mind though--you may have to give up some other goals for him. My humble suggestion is training players to be good in the league you are going to next...not the all-star league.
13) (My first major mistakes) 1-Do not undersell an 18 year old superstar 2-do not buy 20 players, then try to figure out who to get rid of! 3-do not raise your stadium price before understanding what your newly built seats will sell or not 4-do not buy staff until you know what you are doing with the team/stadium 5-do not let your rival beat youon a buzzerbeater then make your players play crunch time the game afterwards for their mistakes :)
Anyway my quick (well long) in-game assessment from a long-term gamer (not this game but in general).