Chicago zoning MFH purchase

[Michael Smith]

I'm looking a t a place that is listed as 7 units in chicago in RT-4 zone

After quick lookup i got contradictory pieces of information

1 up to 3 apartments

2 low density apartments with no number attached to it

so my questions are

1 is is that ok that it is a 7 unit

2 can i reduce the number of apartments to lets say 4 units or do i need special permits to do so

thx