Planning to buy PS4, need a little confirmation?

Hi, guys. I'm planning to buy PS4 Pro in the next few months, there's so much I want to ask but a few research already answered them. So, these are the questions:

1. I know that if you buy physical game you have to insert it everytime you want to play the game although it was already installed on the hard disk. But could you back it up to the external hard disk? Like the base game and the update(s)? I'll decide to go full physical or digital depend on this, because if, just if, the PSN network went down, we couldn't update it anymore, like if I want to play it again in the future.

2. And for the digital purchase, I'm not sure about the resume the huge size of download? Could it really resume the download like Steam?

3. I'm planning to use monitor which doesn't have built-in speakers, and should I go buy those external speakers with the DAC things or headphone? I don't know if the headphone will produce good bass, but it would be more convenient than those DAC things that have so much wires. I mean, what's the pros and cons? And does the headphone drains the controller's battery quickly?

4. The HDR feature could be enjoyed from the HDR10 display, but I saw it somewhere that its brightness must be around 1000 nits, and this LG 32UD99 Tech Spec/Official LG 32UD99 claims it features HDR10 although it just has 550 nits maxed. I'm lost here to know if it affects the HDR feature or what? Or as analogous it would be just like the native 4k and semi-4k (upscaling)?

I think that's enough for now, and thank you for the time.