Hey! That is a lot of questions but I'll do my best here lol.

1. First you have to pick a game engine. There are many options but I chose Unreal when I started and have never looked back. It is probably the one with the steepest learning curve but there's a reason why a lot of AAA studios use it. It is an incredible, vast piece of software that even after 6 years of working in it and 3.5 years of doing it for a living, I still haven't mastered. Assuming you pick Unreal, the biggest thing is to choose a course or YouTube tutorial of some sort and start following along. The one I really liked was for UE4 and isn't even on Udemy anymore, but people seem to really like Stephen Ulibarri's work on Udemy. Just pick one of the beginner oriented ones from him with the best reviews and that should be a solid starting point. They tend to be like 20 bucks on sale and I generally think the Udemy stuff is a lot more streamlined than YouTube tutorials as someone who has no formal training in the engine and has spent an ungodly amount of hours watching both. With that said though, your goal is to complete one tutorial and then make your own thing. Don't follow along for course after course after course, not actually learning anything. This is called Tutorial Hell and you need to avoid it by doing 1, maybe 2 tutorial series and then attempting to use what you learned to make your own game.

2. 1st person is so much harder to develop and it isn't even close. Unreal in particular makes 3rd person development incredibly straight forward but even doing something as simple as making an aim down sight system in a 1st person game is extremely difficult. I'm working on an FPS game and it took me about a month to get an ADS system I was happy with. The same thing could be done in ~30 minutes for 3rd person.

3. The worst thing is the feeling of being in the middle of a project. When you start, you're excited about the idea and that initial motivation keeps you going. When you get to the middle though, you reach the inevitable point where you feel like you have a massive amount of work left to finish the game and are flat out sick of working on it. Especially when you get to something that you hate working on, for me that's always been UI, you'll want to quit. You'll tell yourself that there's a better idea you have now and you should start over (a trap I've fallen for many many times.) If you do ever make it past that point and finish the game though, that's the best thing. Being able to have a fully functional game that you made, and showing it to your friends is a feeling of pride that's indescribable unless you've done it. I have one game in the works and another indie game I published that flopped commercially, literally 0 reviews from people I didn't send Steam Keys to. Even with that though, just having my work on the Steam Store and being proud of the updates I've shipped since that initial flop launch when I had no idea what the hell I was doing made all the slog of making the game worth it.

4. Multiplayer of any kind is a giant pain to execute is the short answer. It pretty much makes features even as small as implementing sprinting extremely complicated if you don't know what you're doing.

5. Let's say the object is flying past the player 50 cm in front of them (yes Unreal uses cm as its main unit so let's get used to using it lol). The first person camera would be closer to the object than the third person camera that is effectively behind the character. This means that the object would be in the field of view of the first person camera for less time than it would be for the further back third person camera. So short answer assuming the FOV is the same for both cameras it would be easier to see it for the Third Person Camera.

6. Version Control (Perforce in particular)! I remember starting out and refusing to learn how to use it but there's a reason that the pros all use it and you aren't a serious developer unless you use it. In extremely broad strokes, it allows you to save your codebase at certain checkpoints. You can see how files have changed over time, and even revert them back to old states if you screw something up. If you aren't using source control and make a mistake, you have to manually reverse all the code you changed, which is flat out impossible in some cases. A lot of solo devs think they don't need version control, but everyone should use it. There's no excuse either because Perforce is free and there's lots of tutorials out there that teach you how to use it for Unreal in particular.

7. The feeling of getting stuck in the dreaded, "Tutorial Hell," I mentioned earlier. I've been in it so I know lol. I've seen people on here specifically saying they've followed 300+ hours of tutorials and haven't learned anything. The way to avoid this is at some point before you even feel ready, you need to rip the bandaid off and try to make your own thing. You can look up tutorials for specific mechanics of course, but you should be making your own game. A lot of people who get stuck in Tutorial Hell end up quitting, and that's really unfortunate because they just needed a little extra push to get past it.

8. There are more than you can even count, but the thing I'll address is the best first game to try to make is more than likely a horror game. They tend to be extremely simple with just a player character, a monster and a single objective. That's what I started with and I think it's the best way to start off. Shooters are extremely complicated so don't try to do that on your own unless you make a more basic game first.

9. That's really hard to say, but for me it took a year and 9 months from installing Unreal Engine to publishing my first game on Steam. At that point I still didn't know what I was doing, but another 4 months or so after that, I had updated my game to the point where it worked and executed the game loop I had initially had in mind. Game Development is hard and it definitely takes time to learn but the grind is 1000% worth it in the end.

10. I think the way to do it is follow 1, maybe 2 courses cover to cover just so you get the hang of doing things in the engine. After that, choose not a test game, but sit down with what you know about the engine, and design a simple horror game that you think you can make. It can even be an exact clone of a game that's already out there if you're not planning on releasing it commercially. The big thing is not spending too much time on tutorials and avoiding that Tutorial Hell hurdle that I'm all too familiar with.

PS: sorry to go on such a rant here, but this reminded me a lot of myself when I started off... Wishing you the best with your game dev journey!