My brief solution to obtaining this achievement and 100% the game.
Clearing all Pegs I found Gnorman to be very efficient in taking out a vast majority of the pegs in each stage due to his uber volt ability (take note that its one shot). If for some reason Gnorman doesn't seem like the one that is the most suitable for the current stage then pick Berg as he is just as good and able to take out multiple round pegs if they are hitting each other with his special ability, deep freeze (which activates when a green peg is taken out and will last until the end of the next turn). It's all about trial and error, find out the angles and learn how to take one peg out at a time and get it into the free ball tube. Also make sure you stay away from the last orange peg as you don't want to accidentally hit and have to start all over. Trust me it happens a lot.
Getting the Ace score. I didn't even realize this method until I came across this in the end. I thought Luna was a useless character meant to rack up some points with her ability but no she is broken lol what you have to do is in each stage that you are having difficulty getting the top score in, is that you have to take out all of the orange pegs first while leaving 1 orange peg remaining. Also make sure you have 1 green peg available for access to Luna's broken ability. When you are at this point of the stage the point multiplier is set at 10 and taking out the orange peg with her special gives the ball the opportunity to take out each individual shadow peg that your ball runs through, after the final orange peg is hit. This will give you 1000 points for each shadow peg hit plus it being the final shot you will just be overloaded with points for an easy clear on the ace score.
3rd objective is usually very simple and doesn't require much effort.
The video below is an example of what Luna can do with getting the ace score. Its just an example of how she racks up points.