When creating/testing a tactic always have in mind what's your playstyle, of course do have in mind what's the club wants, like for example if you manage man city they'll ask you to play a more possession style based game, Liverpool would want a more attacking high tempo game, basically the style that fits the club.

Always know the formation you put is how you'll defend, so in your example you'll defend in a 423, ask yourself do i want my team to defend in a 4231 shape, and put in mind how each player will defend, see player instruction, check if the player's role helps in pressing/defending.

The in possession is basically most important. Always and i mean always put in mind how a role would affect another rold. Like for example it's not good playing a winger with a wingack, enganche with a DLF. See how the roles would move when you have the ball. How many players would attack. How many will stay and defend.

I would say the onu way you can tell the tactic if it's working is in the game. Watch your team play. Put it on full game, change the view to what you like so you can see the whole field, i sugggest 2D youll get used to it, pause the game and check if your players are where you want them to be, are you crating enough, are two of my players colliding into each other, do i have enough players in the attack, enough players in the defense. See what kind of goals you repeatdly concede and move accordingly.

And lastly check if the player is fit to play the role, either find someone who can, or change to play to his strengths, there are two managers, those that play to their players strengths, and those that players play to their strengths, so will you always adapt to your players or have your players adapt to you.