Hi

I've lived in an apartment all my life, and my parents don't have a lawn either so I'm very new to this.

We just sowed our first lawn. The grass has been sprouting for 7 days now and we're noticing some problems: http://imgur.com/gallery/jRSG4GJ

It's a new house built on an area where there were previously greeneries. So there has never been a lawn before, just weeds and wild plants. We had all the leftover bricks and mortar removed and tilled some compost into the ground last year. But we were too late to sow any seed in fall. With the whole corona crises things were too hectic in spring to sow, so we manually kept the yard as weedfree as possible in the summer.

12 days ago we sowed the lawn. We rolled the earth with a heavy roller before, sowed using a seed spreader and then rolled again.

The things I'm wondering about are:

1. The sprinkler doesn't have enough reach, but this is something we can fix with more sprinklers. I think we need to wait for the current grass to grow stronger to dig in it and add more pipelines? It's going to rain the next 14 days, so the rest will probably sprout in the coming days?
2. There are also bare patches where the sprinklers do reach. Despite seed laying there. Will these patches fill in later? Do we need to reseed those patches? When can we do that? Since we can't walk on the grass now?
3. It's also been raining the last two days and suddenly we have two small "sinkholes" how do we fix this? Do we toss dirt on it now? Or wait till the grass is strong and try to push dirt under the grass there? Or refill that part and reseed?
4. If the grass isn't growing evenly, when can you first step on it? When do you mow? When the majority is 8 cm? After 4 weeks?

Help?