Could you help with some Japanese grammar?
(excuse the lack of accents on some letters - I haven't go them installed)
1. Kore / Kono / Sore / Sono
Kono okashi ikura desu ka?
These cakes, how much are they?
Kore o mittsu kudasai
I'll have three of these
Q. Is there an implied 'ones' in the second sentence - making it kore and not kono?
2. o
Kohii o mittsu kudasai
(Can I) have three coffees please?
Q. Is 'o' simply a particle marker connecting subject and adjective? Or does it have a specific translation?
Soshite shingo o migi ni magatte kudasai
Depato no mukaigawa desu
Q. Why not 'no' in the first or, vice versa, not 'o' in the second?
Q. Is 'ga' 'mo' wa' other example of particles? Are there many more and are they always used in the same way?
3. arimasu (please explain!)
ga arimasu ka (do you have)
iroiro arimasu yo (have all sorts)
hidarigawa ni arimasu (located on the left-hand side)
Q. What is the best way to interpret 'arimasu' (I though it was the verb 'have')? Or should I simply just know the phrases rather than try to break them down?
Any help would be much apprecited. I'm currently working through giving directions in Japanese and my head aches with the structure of the sentences!

Anne