Noun plurals

[Rexxo]

Hi,
I'm a beginner in studying Spanish, and now I just got stuck in this little part of the grammar: the plural of nouns.

I've read on a site that nouns ending in a vowel or "é" add "-s". Also, nouns ending in a consonant add "-es". These are the two main rules. Now, the same site says that a noun ending in a stressed vowel other than "é" adds "-es". But another site says that nouns ending in "á" or "ó" add "-s", just like for "é", thus invalidating the first one, and that those ending in "í" or "ú" can add both "-s" or "-es" (jabalí -> jabalís/jabalíes). What are the truths?

Also, a site says that nouns ending in "ión" drop the tilde in plural. I've seen nouns dropping the tilde even if they don't end in "ión", but just "ó" and a consonant, no matter whether "n" or something else. When is the tilde dropped and does it concern only "ó" or it's the same for the rest?

And the last one: I've read that the nouns ending in "x" don't change in plural, and neither do those ending in "s" if the emphasis is not on the last syllable. But what happens if the emphasis IS on the last syllable or it is a monosyllabic word?

Thanks for your time!

[ElijahAR]

Hello!

Regarding your questions, I think the best and most trustful resource is "La Real Academia de la Lengua Española". It is of course in Spanish, but I guess the examples could be useful and sometimes self explanatory. 

 Reglas de formación del plural

http://lema.rae.es/dpd/srv/search?id=Iwao8PGQ8D6QkHPn4i

Be careful with the counter examples. They are highlighted with red "x" marks. Also, notice that some of those rules could have been updated more recently. We would have to double check. Please let me know if you need help with the analysis of the use cases of the plural you mentioned in your post. 

¡Saludos!