On-board USB interconnection
I've more deeply studied the field, and found that 15 kOhm pull-down resistors are required to hold the data line at 0 V (D- in the full-speed mode or D+ in the low-speed mode). In my particular case, all devices are full-speed, so I will try to use them on the D- lines. I still not figured the role of the series resistors, but there are built-in resistors in CP2102 and I will add 22 Ohm resistors to the lines to my uC, just in case.
CP2102 and ATMega32U4 are both have pull-up resistors on their D+ "inputs", it tells the downstream device (USB Hub in my case) that it is a full-speed device.

So, I will try to use only one pull-down resistor and will post here results, but, by now, my advice for the on-board usb interconnection is the following:


carefully read the documentation on the upstream device internal USB transceiver circuit. What components it already have?
if some external resistors (series and pull-up) are required by the upstream device, use them
use all resistors (series and pull-down) on the down-stream termination
capacitors and ESD protection are not requiered