I haven't worked out whether buying the equipment actually makes an appreciable difference yet. Not that it matters now since my team is maxxed out.
Bribing and drugs shouldn't ever be necessary in the top league.
Buying better players is a real money saver. I absolutely refused to transfer though, for personal preferences. I won't give advice on what to develop first as your aim would probably be to develop all round complete players, yes?
My take on certain formations are as follows:
Wall: You need to either outclass your opponent or be confident of your ability to use this effectively. If you break through lines it's great. If you get broken, it's disastrous, especially against another wall, attack or goal hang formation. Works best in early divisions, but I'd recommend looking to other options in Div. 1.
Narrow attack: Is good for going straight up the middle. Most of the AI teams are weak against rapidly passing direct attacks except the fortress and counter-attack formations, which require you to go in diagonally.
Counter-attack: Requires a bit of patience. It's best to feed the ball to the men in the back so you can pass forward rapidly when attacking and retreat quickly when defending.
I don't use any of the other formations, so I can't comment on them.
For many of the formations, if your throw is good, it's worth bouncing the ball diagonally off the wall from just behind the halfway line for a long shot at goal.
Goalie (#1) AI is a bit funny. They run away an awful lot. But don't try running into them head on because chances are you will lose. If your goalie does get the ball and has an opening, milk it for all its worth!