How many LEDs can I connect to each attiny85 port?
All of the electrical limits are given in the appropriate Electrical Characteristics section in the datasheet. Most AVRs have a limit of 40mA per pin and 200mA per "bank", where a bank may include one entire port, one entire port and part of another port, or two partial ports.

Note that running the LEDs with less current or using a driver of some sort will allow you to use more LEDs.