In my opinion Xavi is not really a terrible coach because with what he achieved at Barcelona despite managing a team that is financially struggling he was still able to lift the La Liga trophy. I also don’t want him at Chelsea but imagine what he would be able to achieve with a team that is financially stable. So with that i think Xavi will go to become a good coach in future.
I don't think that Barcelona is financially struggling or perhaps we don't know them as the media potray them. If Xavi is aware of yhe club financial situation, no way they are going to allow him signed Lewandowski and be earning such amount. He was in his prime in Bayern Munich and a great striker but there are other options available for them to look into but yet he went for that and currently earning highest money in that club.
It was not hidden that they were financially unstable because a lot of players had to go through a paycut in their wages to relief the team a little bit, Lewandowski also had to go through aa pay cut as well and not just the players even Xavi himself had to cut down his wages all for the love he has for the team. He was well aware of their financial condition but the team needed a top class striker after Suarez left and Lewandowski made it clear he wanted to join only Barcelona, when he joined he wasn’t at his prime as you said he was already approaching the ending days of his career. His caliber cannot earn lower than what he earns that’s why he is paid such amount and Barcelona desperately needed his services.
Maresca was able to brought Leicester City from the sham manager that made them relegated but you think Leicester will come this far to sell Maresca to Chelsea, if they sell him for Chelsea even at expensive price, who will help them maintain the Premier League tournament. It's better he stick to what he knows than been drag in the mud by Chelsea fans.
They already gave Chelsea the green light to proceed with talks with the manager’s camp and they are already in advanced talks and the deal is likely to happen very soon.