FCSB vs Manchester United

Hello, me and my friends are considering buying a tickets for the FCSB game vs Manchester United. We cannot buy tickets for the Away sections, and we are not sure what will happen if we buy in some other section. Will we be safe there to watch the match supporting United (we are not aggressive fans) and not having any trouble with the FCSB fans? And do you suggest buying tickets online or we will be able to buy them on the day of the mach from the stadium?

Looking forward for your advices