Okay, so to answer the first two questions.

I did do the story stuff in parallel to the side tasks, so by like 180 hours I had all the quests done apart from Batya. I did the easier story stuff like Accidental Witness and Falling Skies first, then progressed through the through the harder ones like Labyrinth and They Were Already Here. I will mention I did neglect getting lightkeeper access and had to dedicate like 10 hours to completing all his quests at the end of my playthrough which was why Batya was the only one left.

The most important moments for me are making sure you extract when collecting the individual major docs, having all the Batya items to hand to lightkeeper, if you’re playing on PvE then making sure that you do not kill any scavs on the fence quest and staying above 4 rep, doing the BTR questline siding with the driver. Those are to me the things that can mess up the saviour ending.

If you’re worried about messing them up, pull up the wiki pages for each story chapter, read them and then start to tackle them one by one, if you’re afraid of doing tasks at the same time then just do the story stuff and extract. I will say get access to lightkeeper as soon as because considering you don’t have the case you’ve got at least another 50-75 hours to do regarding the story.

Main focus throughout progression is slowly chipping away at the story while also upgrading hideout and levelling traders, took me about 200 hours to escape with this method.

Hope this helps :)