Estan pronunciadas las mismas?

"va a ser is more common in daily life, será sounds literary or even harsh because it implies the action is certain, and may sound like an order "No matarás".

Really there is no difference in saying "la fiesta va a ser mañana" or "la fiesta será mañana". I can't see that "order" that you find in that. Both sentences show exactly the same idea and imply that the action is certain.

"No matarás" = "No vas a matar"

Va a ser is immediate future and será is not as immediate. There are not more differences.

At least in Argentina, especially in Buenos Aires, the lost "A" would be the middle one.
"Ana VA SER mamá"
"dijo que las VA HACER mañana"

I think the difference between "va a ser" and "será", is like the difference between "going to be" and "will be".

I'm pretty sure in a normal conversation most people in most countries uses: going to + verb, for example, people always say: ¿A donde vas a ir mañana? instead of ¿A donde iras mañana?, or ¿Que vamos a hacer hoy? instead of ¿Que haremos hoy?, etc.

Yes, because mañana is immediate future. But if someone asks Where will you travell to the next summer he will say: A dónde viajarás el próximo verano? A España claro.

Most people would say, ¿A donde vas a ir (viajar) el proximo verano? A Africa claro.

Don't believe the message above, it's a troll trying to mislead you.
Ir a + infinitive denotes immediate future whereas the future tense (cantaré) means a longer term future. None of them are more frequent than the other, they are simply used different. I'm an educated native Spanish speaker from Madrid and I know what I'm talking about.

You obviously don't know who people talk, if some Spanish student asked "¿A donde iras de luna de miel" (where will you go for your honney moon) he would sound weir, almost all native speakers would say "¿A donde vas a ir de luna de miel?" (Where are you going for your honney moon?) Asi que el unico trolo (no "troll" esa es la escritura inglesa) eres tu.

He would not sound weird, it's a very correct way to ask that. It depends on the situation, imagine you are talking to a just married couple, you'll ask them: ¿dónde os váis a ir de luna de miel? Whereas if you ask a 17 year old girl where she would travel to in her honeymoon you will say: Dónde irás de luna de miel cuando te cases? At least this is the way cultured Spaniards speak, maybe in other countries and social classes they abuse from the periphrastic future,I don't know, just a guess.

Yet another example, if you want to ask a child what profession he would like to choose when he grows up and becomes an adult, you say "¿qué serás de mayor?". Nobody would say "¿qué vás a ser de mayor?".

I disagree, the phrase "¿Qué vas a ser cuando grande?" is very common, at least where I live. (Bogotá)

"Really there is no difference in saying "la fiesta va a ser mañana" or "la fiesta será mañana". I can't see that "order" that you find in that."

The order is that the sentence implies the party will be tomorrow, no matter what. While "va a ser" implies less obligation.
It appears to be a cultural difference, where I live "haré" would be considered more formal and "voy a hacer" less formal. But I think using them to distinguish immediate and not as immediate sounds more logical.
Anayway, whichever you use you'll be perfectly understood.

I really don't see the obligatory tone in será with respect to va+a+ser, the only thing that distinguishes this periphrastic future from conjugated future is the immediateness of va+a+infinitive. If you are not sure if the party will take place tomorrow, the conditional tense fits better: la fiesta sería mañana.

Even more, snce va+ser+infinitive denotes something that will happen soon, at any case this future construction would have a nuance of obligation with respect to será. The verb ir in the periphrastic future means in some way that everything is arranged for the action to happen, since in será the action will happen in an undetermined future moment, but there is not a transition to the future in the present like in the case of va+a+ser.