Well, the issues that you are mentioning are nothing new on these forums as they started last year (around the same time or even a year before that <how time flies :cool:>

. The modern FM gamer has to come to terms with what actually is going on in game terms.
The teams you come up against don't play the same way, and they change tactics during the game (as they do IRL). Appart from this they will also change tactics in conjunction with your winning/drawing and/or your losing form. It is recomended that one builds several different tactics to counter the different situations that the AI will throw at you (at least that is how I've interpreted it).
Getting a club to function is no walk in the park and one has to get all the different aspects right (training, coaches, assignments, shortlists, ect...). It can be hard, but it is not an impossible mission. You can save alot of time using the options in the game itself (F.ex. editing options in tactics, training and so forth). It also takes time (and practice) to adopt your ideologies into the club you are managing (finding the right players and training regimes in conjunction with style of play) and the bigger the club the more you must pay attention to the details.
"Why do my tactics work well against one team and not against another?" is a common question. Well, this should be common sense. Let's take Milan f.ex. They almost never play the same style every game and sometimes they play the "ruthless Italian Counter-Attacking" style away from home to get a result even though they are (on paper) better than their opponent (they'll even do this on home ground to grind a 1-0, and who could forget Juventus back in their dominant period <kings of the 1-0 result>

. But if they need to attack they will play much further up the pitch and that is why I recomend that you have at least two (or more) tactics. Different situations have different solutions and it's about getting them right.
At the start of the game (with low manager reputation) teams will come at you thinking they have a chance against a rookie manager with little tactical knowledge, so it is recomended that you play more cautious. But when you do well you will scare your opponents into playing more tactical (defensive and/or tight) and that's where you must become more daring with your tactics. But you need World Class players (or with potential) to get away with this in the long run if you want to challenge for all honours.
Now, please remember, I am not claiming that there is a "magical" combination when applying the sliders in tactics, but you must keep the different styles of play in the same "mind-set" so you don't start to contradict your own instructions because that's when the AI punishes you ruthlessly (your players will be all over the place causing a total tactical melt-down).
I hope you can use this ideology...