1) Service stations are only good for Washing the under carriage of your car. I emphasized on washing because that's all you should do. Never let them use any type of oil be sprayed on the under carriage. Kills every rubber component in the car. Regarding them washing the paint of your car, well, the cloth they use to do that is also used on the engine bay, the under carriage and is washed on the floor. Imagine all those dirt particles stuck on it while its sanding your paintwork.
2) The car shampoo sachet is as good as the cosmic/kiwi wax they use to POLISH the paint. Stay away from those. Buy a 16oz, 1 liter bottle of shampoo which will give you better bang for the buck. I suggest you get MG's Ultimate/NXT shampoo. Alternatives include NanoSkin cheery suds/Wash & Wax, Turtle Ice shampoo's.
3) Stay away from anyone who tells you "Sir jee, gaari pawlish karwain?" (My urdu isn't great so you need to excuse me). The problem here is that every service station walla thinks that polishing the paint is the ultimate last step product (LSP) to get a perfect paint finish. What they don't know is once the paint is polished, you need to protect the exposed new layer. That's where your Paint Protection products come into play. About silicon, you've done your research, but there are some products that use silicon yet are the best selling on international forums. But the general rule of thumb is to stay clear of anything that has Kiwi, cosmic, car pride etc etc written over it.
4) It dosn't seem to last very long. Hope you find the answer in the above point. About removing any old wax or fillers, you can either go the cheap way and do a surf wash in a service station ( this usually strips all protective coatings on a car or buy a dedicated wax stripper. There is another way, an IPA wipedown. IPA = Isopropyl Alcohol. Simply buy a bottle of IPA ( spirit ), and check the alcohol content. If its 90-99%, mix it with water 70/30 and pour it into a spray bottle. Spray this on each panel after you have washed the car and using a mf cloth, wipe down the panel using straight lines. Thats it, you have a panel that is now bare of any build ups.
5) Regarding claying, the newer alternative are obviously better since they can be handled easily and d the job quickly. A kid can do it, its that simple. The only thing you need to remember, always keep the section you are working on well lubricated. You don't need to apply pressure to remove any surface contaminants, gently rub the clay/sponge/mitt over the paint. Keep a sandwich bag ( small airtight bag ) with you, wear it over your hand and feel the paint. You should feel a significant difference before and after claying a surface.
6) If the scratches are deep enough to have gone through the cc and paint, you wont be able to fix these. The only option is to get the color coded paint for you car and use a micro bush to fix the scratch. You can then wet sand the filled in paint to even it out but wet sanding is something best left for professionals.
7) The two defects you mentioned are very similar and are the reason why the paint looks hazy and not reflective enough hiding the true potential of the depth of the paint itself. There was a thread by mike on AG or MOL, don't remember exactly regarding the differences. You can google it. It should come up. You can go ahead and use compound/polish by hand application. What you need to know is that this way, the results won't be as promising as doing the same work with a polisher. But, its the easy way for a first timer to get the paintwork looking a lot better than before.
8) A filler will be useful if you plan on doing the compounding/polishing with a hand applicator. It will mask the imperfections left behind by the two steps above. Filler's (called glazes) usually come in two forms. For dark colored cars and for lighter colored cars. But there are products which on both types of paint shades.
9) A synthetic protection coating is preferred for lighter shades no doubt. A sealant will only do so much to protect the glaze as it can to hold itself. I mentioned after a few wash's. I wash my cars once a week and the glaze on my car usualy wears off in a month. I do layer the glaze over with the sealant+wax combo. If you don't do that, the glaze will wash away after the first wash. They have zero durability on their own.
10) AG = Autogeek AP= Autopia
11) Most cars from the late 80's came with clear coats. So unless your car was repainted and not topped off with a clear coat, the original paint has cc on it.
12) Regarding the products, you can opt for the meguiars car kits. Look at their clay bar kit ( Or get the autoscrub by Nanoskin ) and their new car kit. You can get the #7 glaze and Ultimate compound desperately.
Hope this clears up your questions.