Different literature reviews have different purposes which my determine what kinds of articles they look for. But for most literature reviews, a systematic literature search should include ALL possible sources and there is no justification to include only articles from "top-ranked" or "elite" journals (such as the Q1 that you referred to). That would be saying that it is unlikely for articles in other journals to have anything interesting to say related to your topic, but you have no logical reason to expect that. Your reason given, "If I include all, it will make my review paper really long", is not an acceptable excuse. Any such review article would likely be rejected for publication by any journal in Q1, Q2 and even Q3.
Moreover, in computer science specifically, you absolutely must include conference articles since much of the best original research is published there.
So, what do I recommend for computer science? If you search only in the ACM Digital Library and including anything and everything you find there, then your literature search would often be considered sufficiently comprehensive for the computer science domain. However, some specialized domains might need additional database sources, even in computer science. (If you want to be really exhaustive, you could add arXiv for grey literature [preprints], but that would probably not be required.)