Ok, here it goes:
1. A good rule of thumb you can use is the following, when you want to say "it's allowed to do something" or convey that idea in English, then use "se puede". For example "Se puede caminar sobre la grama?" would roughly be translated to "Is it allowed to walk on the lawn (grass)?".
Now, when you use "puede", it's simply the verb "can" or "be able to" in the third person singular (keep in mind in Spanish, you also use "puede" to conjugate the verb "poder" when you are using the formal second person "usted".
2. Yes, you are right. You can say "Este plato está muy bueno", "Esta comida sabe muy rico", and if you want to say it's especially tasty, you can say "Está delicioso!"
3. Correct. You can also say "Ella adquirió el seguro."
4. When you want to say "The more the merrier" or "More people, more fun", you can say "Entre más gente haya, más alegre (divertido)." In Latin America you usually say a short version: "Entre más, mejor."
7. Correct (If you are referring to someone in a formal way, remember to say "Tiene cambio para un billete de cien?", for example)
9. Correct, the only thing is that you write "por favor" in Spanish, not "por favour"
10. In this case, I would translate "around" as "cerca de", not "alrededor". So you would say "una estación cerca de la escuela". You can also use "en los alrededores", which means more or less "around", so you can say "Hay alguna estación en los alrededores de la escuela?"
11. I find the sentence basically correct. I would just change this part "... que supuestamente debería estar dentro del equipaje estaba afuera."
12. The sentence is gramatically correct, but if you wanted to say "I will tell you more..." you should then say "Te voy a contar más acerca del tema durante la cena."