"It is my bottle."
Translation:É a minha garrafa.
Everything has a gender in Portuguese. Meu=for male Minha=for female. Normally the nouns ending whit an A will be Female. Minha garrafA. Meu casaco.
Both are equally common. The "a" is not stressed anyway, so in everyday speech you might not even hear it if someone speaks fast enough.
Yes. You would add "a" if you wanted to emphasize that you are talking about your very own bottle.
No, you would need the verb between the noum and the possessive, like in: a garrafa é minha
No. Issa is not a word in portuguese. It could be ISSO. Since, roughly saying IT=ISSO. But in this case ISSO would be used in a ironic/depreciative way. It is hard to explain writing