With that being said, I wanted to replay the game from scratch (regular NG, not NG+). What should I expect while doing so?

I just started a fresh save a few days ago and the game is WAY different than it was at release. Everything feels a lot better: combat, parkour, physics. A TON of new side-missions. I feel like even some of the cutscenes are different.

The UI is still terrible to me, but whatever. Not that big a deal.

There's nothing you really need to know, though, that you won't figure out on your own. Volatiles are everywhere at night. Howlers are out during the day now. Virals spawn in like every 60 seconds whether you make a loud noise or not.

What about the firearms? Are they time sensitive? I mean, are they tied to a timed community event or will I be able to get them in the future?

No, but there is an event running now that puts a free pistol in your stash for a limited time. Claim it before it expires. It will look like it disappeared, but don't panic. It will show up when you've progressed enough in the main story to unlock the "Lost Armory" quest. This is the quest you need to complete to unlock the firearm vendor. It is a permanent addition.

I have 130h and I like the game a lot, but I think the story is pretty shit and they should have focused on gameplay instead of that. And I hate how the special infected don’t come out at day like they did in dl1, goons do come out sometimes but 90% of the time they are surrounded by like 20 biters which isn’t fun. Also the lens flare makes it very hard to play at times.

I love both... you will never beat the first for me personally, but DL2 is finally at an amazing place, and I still think the base game story is better in 2... both amazing games