With the information provided, I can only make overall recommendations. 80 tables is a lot. The most complex model I have built has about 20 tables (including island tables for dimensions and control purposes) and this was integrating data from about 25 different sources. Having said that, 3 million rows and 250 MB is not a very large data set.
You need to work towards a star structure with a single central fact table and dimension tables linked to the fact table. You could also collapse small dimensions (eg containing only some ID/Name data) into the fact to simplify the structure.
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