Laid a rear lawn 15yrs ago. I wouldnt go to so much trouble as this for a front lawn that gets little use but this has lasted brilliant and is one of the first jobs i will do on my new house.
1) Dig out old turf plus a little bit. I had major drainage issues so i dug more than needed.
2)Lay batton frame around edge flush with final height of lawn. I had a slight slope on purpose to encourage rainwater to flow to a drainage channel i put in before my decking.
3) Whatever depth of base aggregate. Dont get it too small like i did as you just move it around. Get decent size stuff. Flatten down
4) Top off with sharp sand and flatten to level with battons.
5) Layer of proper membrane to stop any growth. In truth i have never seen even a single shoot.
6) Fix down with heavy duty carpet staples.
It lasted 10yrs before i had to do a single thing other than hoover it. At 10yrs i ordered a ton or so sharp sand, lifted the grass up and had a day of flattening and leveling. Relaid the grass and its been A1 since.
If you find laying the grass too tricky, do all the work and get a carpet fitter to do the final job if its complicated.