In order to calculate the number of guests that a 300-square-meter cafe can accommodate and the number of places that need to be placed, we need to calculate according to the area and seat layout of the cafe.

A 300-square-meter cafe can accommodate about 1.5 people per square meter.

Therefore, the maximum capacity of this cafe is: $300 \ times 1.5 = 450 people $.

If the layout of 8 people per table is adopted, the number of tables and chairs to be placed in this cafe will be about $300 \ div 8 = $37.5.

Each group of tables and chairs has about 8 seats, so the approximate number of seats to be placed in this cafe is: $37.5 groups \ times 8 seats/group = 300 seats $.