Would you go out with a girl who said in advance something like "I want you to know though that I have a BF", as to say that "we can only be friends".

I said "don't worry, I'm not looking for a GF" but she replied she was relieved for me saying that, such as she understood I only want friendship rather than I only want sex .

Well, there are some signs of interest like she said guys from my place are famous for being good looking and manly (and added "sorry, just can't help not to say that"), but she doesn't stay out late and doesn't drink. So it would be "friendly" afternoon walk in the park, brrr.

Would you go -and would you go if your pal was having a BBQ that same day -?

If I girl told me lets go out but I have a boyfriend, I would say something like well don't bring him that would just be awkward, or something to that effect. I would then go out and see what came of it, but I would split the bill.