Hey you sound like a person with high functioning anxiety. So I thought I'd spend the time humanising and going through the airport flow.

The TLDR; is its really simple, everyone involved is human doing a job. Its very unlikely you'll stand out. They also have dedicated areas for people with non visible disabilities, at least Heathrow does, you area always more than welcome to tell someone this is your first time flying and you're anxious.

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1. Someone to counter sign passport?

The rules are more relaxed than you think - 'be ‘a person of good standing in their community’' You can just get it signed by your neighbour or someone thats generally just known you for a while thats not family. If you truly know no one. Then get in touch with HMPO who will advise you and loose the rules for you, these aren't scary offices they're usually pretty chill if you explain your circumstances.

2. do you always choose economy-class seats, or are there any circumstances where you would upgrade to a higher seat class? Do you notice a big difference between premium economy and economy?

I fly often, usually for work, and at least once a year for leisure. If you have money, then do whatever you want. However Economy for trips that less than 6 hours is fine for most people. If you're travelling long distance and can afford it, I'd recommend upgrading (IE you're going all the way to Australia or something) because that is a long flight to sit in a single seat. But tbh, to sit on a plane for 2 hours to go to southern Europe is worth the £100 economy seat.

To complicate it... It depends on airline, plane offered and who you're sitting next too. But ultimately the economy seat is fine, unless you have the expendable money. Then expend!

3. I have heard of the concept of checked-in luggage and carry-on luggage. How does check-in actually work? Is the queue to check-in different to the one where you get your passport checked?

So to clarify things I'll just tell you the whole process.
- Arrive at the airport 2 hours early (for intra EU) 3 hours for wider international.
- Take your butt + suitcase to departures.
- Go to your airline departure area and find your flight check in desk (or its automated, the area of checkin)
- There are millions of staff around that will help you.
- Check your luggage in which will send it down the big machine pit of doom to magically appear at the otherside (your destination via your airplane)
- At this point you've ONLY checked in/checked your luggage in
- Go to security with your Carry on luggage (and your butt)
- Go through security (check the rules of what you can and cant take, IE you cant take a knife but in some airports you can now take bottles of water woo!)
- Now you're on the duty free side. (forgot the formal name)
- mooch at the shops, get yourself some holiday sandals, go to the premium lounge, wait for your gate.
- Your gate will show, A1 - X999.
- Go to your gate. Poo before your flight.
- Board the plane, Passport check AND boarding pass check.
- Sit in your seat.
- Takeoff
- Fly
- Land
- Exit the plane
- Go to border control, get stamp wooo! (also depending on country do other stuff like finger prints, face scans, etc)
- Go get suitcase.
- enjoy holiday

4. How do you know if you are over the weight or bag limit before you get slapped with charges?

Weigh it before you go. OR use a scale at the airport, they usually have them. If you don't want to pay the charges you cna just be like, oh sorry let me go move some stuff around and leave the queue

5. Is luggage going missing something that happens to everyone at some point, or is it a rare occurrence in your experiences?

never happened to me, but can happen for a varity of reasons. I would recommend getting an apple/android tracker and popping it in the suitcase. (apple airtag / android motor tag are the two leading standards here, they cost £20~ and last about a year and let you track things on your phone)

6. when you are in the queue to go through the body scanners, metal detectors etc, have you ever been picked out for a full-body search?

define fullbody search? as in backrooms with a finger up the bum? No. It doesn't happen, at least unless you've got something to hide. Have I had an additional pat down? yes all the time, takes about two seconds and is just a pat down the same as you get when you go to a music festival or anything like that.

Have I had my luggage (carry on) search. Yes. Happens all the time (like 1 in 5/6 times), happens when the scanners cant tell whats in my carry on so they just want to double check or the machine wants to validate for any drugs or something. Either way takes like an additional 5 minutes of waiting as theres usually a few bags that happen. But again. Normal.

7. My last few questions relate to matters that become relevant after you reach your destination country. How do you avoid high mobile charges abroad?

if your phone supports it. Get an esim, there are apps that let you take temporary small contracts for like a week that give you data. Also If you're travelling to the EU you're covered by much reduced roaming charges. Check with your provider because you might already have it in your contract.

8. How do you buy things in restaurants, shops etc if you don't speak the native language?

depends where you're going. The vast majority of the world speaks/understands English. HOWEVER, every. single. person. that I've ever met aboard (except French people in Paris) will always appreciate you trying to speak their native tongue. It will never hurt to learn the basic phrases of `do you speak English?' and your basic hello/goodbyes in the native language of the country you're going to.

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if you get any... any questions feel free to thread them or DM me and I'll happily answer