I mean sure why not but if you only want a limited amout of chapters it might get hard. Also, you need to have the plot to do so. I'd rather read more chapters than super long ones. I like when they have a word count of 4000-6000 each, but that's just my opinion
... Expanding an 8.000 fic (I take this is the completed version?) to 50.000 seems pretty ambitious to me, to be honest. Is the potential there? If the plot allows for such an expand, sure, go for it, but do not write just to make it reach 50.000 words. Why do you want it to be that long?