Ok confession time, I still struggle with my first lethal community even after making it as easy a start as possible. The two main problems are A) how much time I've spent on the trivially easy normal difficulty with max level survivors and B) I watch a youtuber called 'Git Gud Fox' who has spent so much time in lethal that he sometimes does challenges to spice thing up and I think that made me overconfident. The other day I lost a survivor (according to the achievements, the first survivor I had ever lost) trying to take care of an infestation who managed to get overwhelmed even though she had a pyro launcher equipped.
I dunno, it's just nerve-wracking. I can barely stand to let a survivor that isn't a red talon leave my base, and even they feel fragile. The Impaler guzzles gas like mad but it's the only thing I feel comfortable driving and it eats repair kits like candy even doing my best to avoid frontal hits on zombies.
So, I had Nightmare down pretty good and had stuff like you describe. Felt Red Talons were unstoppable, had the game on lock, etc.
But I had read enough to know that Lethal is its own animal, so I rolled up 3 random survivors....good enough that I had my bases covered for skills, but not good enough that I'd become attached to that. And I started with that.
I made it half an hour.
Holy shit did I learn a lot in that half an hour. I had considered myself a pro at the game, and that half an hour taught me that I didn't know shit. When you have to start from zero, the game goes out of its way to show you priorities.
First of all, if you get a material ruck, don't deposit it when you get back to your base. A quest will spawn immediately giving you some. Huge help.
Before that, however, is that first feral. Heavy weapons are your friend. If you have one, great. If not...the 2 AI's are gonna need to pull their weight. You can lose right there without really doing anything wrong, and that's what makes a good zombie game, imo.
I use heavy weapons almost exclusively, because you can stunlock ferals with them. Swords are great for the frontal execute, but they don't do shit vs Ferals. You've gotta have a plan for ferals, everything else you fight is the same, but never leave home without a heavy weapon.
The next thing you need is infirmary 2 for healing, asap. Build it before anything else. And plague samples. You need lots, or you're gonna die.
You've gotta sneak on lethal. All over the place. You've gotta learn to park on lethal...always park with your hood up against something and NEVER enter your car from the driver's side. The zombies will rip your door off and you out.
Infestation? Firecrackers and molotovs. All while crouched. You don't need to expose yourself any other way.
Lethal is the same game, only it really punishes sloppy play. After that though, it's very rewarding, because every ruck is something you earned. It wasn't just given to you.