"I will always love you."
Translation:Eu sempre te amarei.
I don't think you can do that, grammatically speaking. Because from what I understand, when you have adverbs such as "sempre", then you have to use the próclise form (where the pronoun comes before the verb), even if the verb is in the future/conditional tense. There are other conditions that call for the próclise, such as a verb being in a negative form. For example, "Não se pode dizer..." while "Não pode-se dizer" would be incorrect. In my opinion, in this case, "Sempre te amarei" would be acceptable.
Here's a link to a question being answered that's related.: http://www.ciberduvidas.com/pergunta.php?id=6851
And more general information on pronoun placement: https://pt.wikipedia.org/wiki/Coloca%C3%A7%C3%A3o_pronominal
1) When you make up a sentence expressing future with "ir", the next verb is in infinitive. Actually, everytime you have two verbs together, the second one is in infinitve. (eu vou amar...)
2) Yes... we always mixing the pronouns up. In spoken language that's acceptable, not the same when writing, because you have to agree them all.