Of a truth Xavi is not really an experienced coach and had only had good experience in the Champions League as a player than coach, it was proven last season when they got demoted by Manchester united in the round of 16 to the Europa League but they still could perform well in the Europa League or even try to win it, atleast he managed to lead his team to winning the Laliga trophy and I think he should be given more time to build the Barcelona team, he's had an experience last season and could perform better in this seasons Champions tournament.
Though I can't vouch for them to win the Champions League under Barcelona but I expect them to perform better than last season and even go beyond the round of 16, my only fear is Lewandowski's form and if he continues miss chances it could affect their performance when the Champions League starts, however their rivals Realmadrid would have a better performance and probably reach the finals this season.
Of course, Xavi experience as a coach is still quite minimal, because he coached Barcelona for the second season after his first season successfully led Barcelona to become champions in Laliga. Yes, as a player, of course he had great experience in the past. But for coaches who have long experience in the Champions League, of course these figures are Pep Guardiola and Ancelotti because both of them already have long experience in this prestigious competition.
So for that, if Xavi can bring Barcelona to win the ucl, he will definitely make new history in his coaching career. But this season, of course, there are many big challenges that must be passed by Barcelona in the Champions League because other big teams certainly have the same goal to be able to win the UCL trophy.