Papers published in top journals are not uniformly good. If the paper is of significantly good quality, it is better to publish in a top ranked journal than a number of publications in average-ranked fournals
That depends on the research paper aim(s), and if they are similar and can be compiled into one "stronger" publication in higher ranking journal that may yield more citations than fragmented publications.
But if the Aims are distinct, I suggest to make into several papers, and try the best amongst them in the higher journals.