I'm going to replace all my Access Point with mikrotik hardware, especially to implement Nv2 protocol.
CPEs are increasing very quicly and TDMA seems to be essential.

Reading wiki I read:

"Nv2 network will disturb other networks in the same channel"

Now, my 4 AP and 120 stations share the same frequency into PtMP network. Will I get in troubles using Nv2 protocol?

Then I need some help to setup both AP & Client sides.

The NV2 protocol doesn't cause trouble. The trouble is that the use of another radio in the same frequency space will be noise to the other radios. Choosing NV2 or 802.11 or any other protocol will give you the same interference.

Ok I thought with nv2 enabled interference could be heavier.
Anyway is it enough change wireless protocol to nv2 for client and Ap or I need to set up other parameters like tdma period side, nv2 queue count etc?

Just setting the wireless protocol to nv2 is enough. You can also use the nv2 pass phrase key if you want encryption.

I will lose default wpa authentication?

Yes, you will loose default WPA encryption when you use NV2. The NV2 protocol does not use the default security settings, it will rather use its own security settings configured under the NV2 tab (nv2-preshared-key)