Lawn help... And lots of it

Finally getting stuck in to our new garden but having done some research have discovered that it's in a bit of a mess. We have a largish lawn that is currently overun with,(amateur guestimates here), moss, catsear weeds and chapher beetles.Poor drainage is an issue too as we do tend to have some pools on the lawn in heavy rain. The grass tends to be spongy in areas, yellow in others,bald in parts and then lush a green around the edges. We also have these bugs that on close inspection are rife in the grass, which I read could contribute to some of our issues. I know this is a really tall order but would really like some advice on where to start.or to just rip it up and start again, but I do like a challenge . Thank you in advance. X

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