Translation:I am going to love someone that loves me.
It certainly can be, but "that" is also acceptable and widely used.
"In fact, people have been using that for human and non-human references since at least the 11th century, and that is handy if you want to talk about both a person and a thing." (http://blog.oxforddictionaries.com/2012/09/that-who-which/)
Could anyone of you please check if the translation "I will love anybody who loves me" or something like that was 100% accepted?
Why does the hint translate:
alguém = someone, somebody, anyone
if "anyone" is ONLY "qualquer um"?
It depends on the sentence.
Anyone = qualquer um, qualquer pessoa (affirmative sentences)
Anyone = alguém (interrogative sentences)
Anyone = ninguém (negative sentences)
I wrote "Eu vou amar alguem que me ama" which was marked wrong. They want "...que me ame" which appears to be subjunctive. Is the subjunctive mood required here?
No, but it gives a slightly different meaning. Your answer means something like "I will love someone that loves me (right now)." It is like you already know who that person is, you are just not directly staring who that is.
What would be the sentence in portuguese for "those who love me" (i.e. possibly more than one person?).
Depends on context. If you're talking about specific people that you already know, then use the indicative. If you're talking about hypothetical people that could potentially love you someday, then you use the subjunctive.
I think it is wrong, yes. "alguém que me ame" is a relative construction, "somebody that loves me", and is the direct object of "amar". Who am I going to love? Somebody that loves me.
For your meaning (or for "I would love it if somebody loved me"), I think that in Portuguese you'd need to say something which literally means "I would love that somebody loved me" - "Eu adoraria que alguém me amasse".