I would suggest to put either cm or dm to more creative role, since your idea of possesion game will not properly work this way. I prefere to have my CM as BWM as he will press higher up the field, and on DM to have regista, since he will also push higher and be available for passes, but also bi more agressive with ball and create some chances for you. If not, DLP with defend duty is ok, as all higher placed players will always have option of back pass ,but either way, game will then see your DMC as main creator, and your heat map will be closer to your half. With regista, your main playmaker will be still your AP, and your possesion will be higher on opponent teritory.
Also, good solution for you in this setting is to have yoru rcm to be BWM since you have extremly ofensive RB. This way, he will cover his trips to offence.
Now, best way to achive this is probably to have Gerard on DMC and Leiva on CM, this way you will have creativity of Gerard as well as his good long shot ability, you will still have Coutinho as your main playmaker and Leiva will cover main hole in your defence in this formation, so his quality would be better utilized.
Now front three. You have both of your players on left on support. This mean there will be no crosses or runs from left. Your two players will pass each other endlessly, or they will try to send trough balls to your striker. On right side, you have total oposite. Both players will try to driblle trough opposition defences and both will be more cutting, so you will loose width here. I would suggest to put your AML on attack duty, and Your AMR on support duty. This way they can cooperate and create space for each other, and you will have much more witdht.