If the questions have become stupid and repetitive to you, I'm assuming you learnt the answers a while ago, some people are new to Thailand, and obviously don't know the answers, the same as you didn't, when or just before you first arrived, so understand everyone needs to learn.
absolutely, they purposely make it a long draw out process, by just sending you from one desk to another, to "check your documents" when they know everything is in order, at the first desk you go to, queuing up every time, I have experienced this myself, being in there for hours and hours, that's what they want you to say "never again" and just pay an agent, jomtien immigration have said for a long time, only come for a 30 day extension, when you have a week or less on your current stamp, but I've heard of people being sent away, and them only being able to do it, on the last day of expiry. 😳
Jomtien can sometimes be a difficult office for doing things yourself, (because lots of agents use it) you might get lucky, and be in and out in an hour, but if you go on a busy day you could be in there for hours!! if you don't want the hassle just use a recommended agent, there is an agent in an office, actually inside the immigration office at jomtien, as you walk in they are on the left hand side, you can do all the photocopies and photos in there, and then if your struggling, you can ask them to assist you.
so you didn't use an agent to get you back into Thailand?? Did you get a denied entry stamp at the nong khai border?? What happened when you went back to the Lao border, after being denied entry into Thailand?? Did you need to buy another visa?? When you checked in for your flight to BKK, did they ask for a flight ticket leaving Thailand?? I've been wondering how you got on.
there is a standard priority lane, it seems to be for elderly or disabled people, or if someone has paid extra to basically jump the queue, the op used an agent to guarantee his safe passage through the immigration, and back into Thailand, they two completely different things.
If you require any visa or extension of stay, it's always best practice to visit the immigration office you will be using, and ask for a list of requirements, because with immigration offices it can vary slightly from office to office, most will require a printed receipt of the TM30, or I've heard of some people just taking a photo of the screen after it's been completed, and printing it themselves, a while ago some immigration offices didn't require it, if there was a recent one already filed in the system, another option would be to pay to stay in a hotel for one night and get a TM30 from them (check with the immigration office some won't accept one night) depending on the office you use sometimes it's just not worth the hassle, you can just hand your passport to a visa agent and they will complete the whole process for around ฿4000.
there are lots of agents in Pattaya that can organise an ED visa, it is usually a similar price as dealing with the school direct, they must give the agent a discount for recruiting students, the agent deals with everything regarding the paperwork and actually getting the visa stamps in your passport, it's actually easier than chasing the school for all the paperwork, and visiting and dealing with the immigration yourself.