You never got an answer but I'm wondering the same. Kind of a weird example, at least in that direct translation with "but" sounds a bit weird. "But rather" would probably make the most sense in English. My Spanish is rusty but I definitely would assume this isn't but as in pero as you said.
I think this (current action) is the most natural interpretation. It was said above that it can mean "I don't eat meat but I do eat cheese" - I beg to differ. אלא is used to mean "contrary to what you might think". In this sentence, it suggests that the interlocutor presumed the speaker is eating meat, and the speaker corrects her. It can be about a habit, but I'll need to work harder to imagine a context where it would make sense...
It's a strong adversative, as YardenNB says. I discuss the background here: https://forum.duolingo.com/comment/16336259/לא־אני־אלא־הוא
It's a great question. I'm just a learner, but אלא has the sense of "but rather" and so there's a strong contrast (Spanish sino). So it seems that אך or אבל would work better for that sense of "but." Another word would be helpful to indicate the idea of "but generally" such as אך לרוב. Thus, אך לרוב אני אוכל בשר.
Living in Israel, I can tell you we run the whole gamut. I can draw a rough scale of religious laws/habits. Let's say that there are the "100% religious", who strive to obey the 613 commands; Of those that don't, many would still go to synagogue on Saturdays; of those who don't, many would still put on yarmulke at a funeral; of those who don't, many would still fast on Yom Kippur.
Now with kosher eating, it's similar: most of those who would wear a yarmulke only in the Shabat visit to the synagogue, or wouldn't visit a synagogue regularly at all, would still insist on buying and eating only in places with kosher certificate. Of those who don't insist on a certificate, many would still not eat dairy and meat. Of those who would, many would still avoid chametz on Passover; of those who eat chametz, many would still not eat pork.
Interestingly, of those who would eat dairy and meat together, many would be aware that they do. I am in this group.
They don't mean the same thing.
- חוץ: It means outside, and you were probably referring to חוץ מ־ which means except (lit. "outside of"). For example:
כולם לובשים אדום חוץ ממני – everyone is wearing red, except me
- אלא: It means but, as in this sentence:
אני לא אוכל בשר, אלא גבינה – I don't eat meat, but cheese