Asking /may/ using /posso/ is 100 % polite!

Using /potrei/ is not good for asking permission, as Anna arleady explained.

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A related subject is the use of /voglio/ and /vorrei/, in which case /vorrei/ is the polite form,

but these facts just follow strict logic, as /vorrei/ has an implicit (ailent) part that says: se a te non dispiacesse (subjunctive mode).

Examples:

The silent part is written in square brackets.

- vorrei un panino [ se lei (the seller) fosse d'accordo]

- voreri uscire una sera con te [ se anche a te piacesse l'idea ].

- l'anno prossimo voglio studiare il cinese (here /vorrei/ is not appropriate as the speaker is just stating his will that should not interfere with anybody)

1. I don't think the waiter said that your meal is molto bene. Maybe when you ordered the dish he said: molto bene, as saying Ok, all right, ..

2. Potrei is used in sentences in wich you make suggestions, :" Il prossimo fine settimana potrei andare al mare". "Devo fare un regalo alla mia amica che ha il compleanno. Potrei regalarle una borsa."

Posso is more something that you can do because is allowed. As : "Sull'aereo posso portare una valigia di massimo 15 kg" " Posso portare il mio cane a casa tua? " Posso usare il Suo bagno?" You can use potrei in questons as Potrei usare il Suo bagno? It's true that it 's more polite but it's unusual. It's polite also if you say posso :) 

3 rosso is a color but if you use it describing a noun it becomes an adjective so you have to change it as you say : la casa rossa, il fiore rosso, i gatti rossi ecc 

Hello,

i agree with Gabriele for points 1 and 3.

About "posso?" It's a kind of short question, for exemple a long sentence should be "posso accarezzare il cane?" if you want to do something that need a confirmation you should use the form presente.

Condizionale is better to describe an intention that can asks for a condition.

hello!

1- he said "molto bene" because he was a judge, it was as he said "you have done very well" so i think it correspond to your "definition"

2-i can't really explain this in english, as you can see, i'm not good enough but i try: you can use equally the form "posso?" and "potrei?", usally "potrei" is most polite then "posso"

3-"do I say rosso, rossa, rosse, rossi (depending on agreement with the noun)" yes you say it in the right way, isn't correct using only "rosso" 

I find reasonable the above explanations about that "molto bene" of the waiter.

Nontheless, the couples buono/good and well/bene don't match perfectly.

So for instance, expressions like "to be good for" or "to be good at" can be translated in Italian as "andare bene".

Or, if someone asks you "come stai?", you can answer "bene" or "non molto bene" (while in English you could answer good/not so good).

Furthermore, "good", as a noun, can usually be replaced with "bene" in Italian.

Surely there are other differences that now I don't remember :)

But anyway, are you sure that the waiter was really Italian? :)