There is an option to send only one coin but in that case I would have to pay a small txfee (still duno if I have to pay it again to get my funds back). Am I risking to get back a pairing coin instead of BNB? Like BUSD in your example.
It's the same thing I said above. If you only add BNB, half of it will be sold for BUSD so you can add 50% BNB and 50% BUSD. You can't run from that since it's an AMM.
So as I understand, the biggest risk is that I may end up with a pairing coin while my initial coin is growing, right?
Yes, so you "lose" some of your potential profits.
Is there any freeze period for withdrawals and how often they distribute rewards?
No freeze period, AFAIK.
The rewards are distributed constantly. If you have a big deposit, you should see it growing almost in real time (as people trade).