I would remove it grass has a way of coming back to life .

yep, there is a thread where someone was redoing their backyard as a garden. lots a good info. Mainly we said do one part at a time, keep rest mowed low til you get there keep black plastic and all materials on part you plan on working on next. This will help destroy it then you can get someone to help dig up and create a garden on the are you are working. So you need a plan first. Did one about 25 yrs ago in FL, made an english garden fl style, in the summer yet. horrible drought last 2 years i was there, people spray painting the grass, only watered every 2-3 weeks. And this was with an assortment of plants not just the grass, and native things.

Thank you!