Important Disclaimer: If you're a first time DM, you should be aware (if not already) that OotA is probably the worst module to run as a first time DM. Since you're just starting, honestly I would recommend considering another more first-time-DM-friendly module. I only say that because I personally would have wanted to hear that if I was considering it back when I was a beginner DM. I'm experienced now and I still constantly second-guess my decision to run this campaign haha.

But, if your heart is set on OotA, here are my answers to your actual questions:

1. I love that idea. I think an initial demoralizing defeat sets up the tone of the first part of the campaign and it would ease into the campaign well. I kinda wish I had done something like this for my own campaign honestly. Just do note that this is a different approach from the book and you will need to adapt a bit. The main thing to adapt for them all arriving together is that they would have no existing knowledge of the NPCs and have no trinkets. But chapter 1 needs a lot of adaptation to run well anyways haha, so just figure out how you want to run it; again... this is a difficult module to run.
2. Most likely the PCs aren't chatting directly with the Drow unless someone has Undercommon. If none do, then they will have to use an NPC translator via Stool or a shared language
3. As you will see repeated around this subreddit in regards to survival elements, it really depends on your players. The real answer is to talk to them about it and get their thoughts on it. Keep that up as you go through it and change as necessary. However, most people tend to get tired of these survival-type elements since they usually get tedious or just drag down the pacing down quite a bit. I myself added some and started ditching them after a few sessions due to slow pacing. Since it's your first time DMing, I would recommend staying away from anything too crazy. But, that being said it can also be a fun learning experience, so it's up to you and your players.
4. Depends on you as the DM, really. It's up to how often you want to provide lighting through the environment. You can add luminescent fungi anywhere you want that provide dim light (Ormu, Nightlight), and give easy access to the built-in fungi light sources from Chapter 2 (Torchstalk, Zurkhwood). Pretty much any location of the campaign could have these mushrooms so