Personally i would use VAR like the review system in Cricket. let VAR monitor offsides like DRS monitors no balls, when a goal is scored quickly check the offside and say yes or no.
For the other decisions each team has 2 challenges, so a player will know when he has been fouled, or if something has happened off the ball and he is responsible for the challenge. If the challenge is frivolous then the team loses a challenge if it is correct they keep it. If you are wasteful and then a certain penalty is denied at the end, then it is the teams fault for wasting the challenge.
Yesterday you saw teams playing up to the system knowing the referee would then go to check, with no consequence to the team.