It turns out to be a very early fight for him and for sure Khamzat Chimaev needs to gain weight in order to contest Kamaru Usman with his weight and this is on short notice I truly believe that this is the only advantage that Usman has against Chimaev and for me this is a great opportunity for Chimaev to test the waters on this division they surely need to gain weight so he can clash against Kamaru Usman for sure
The Chimaev vs Costa fight was held in the Middleweight class. Chimaev has certainly gotten used to this weight. Even though he once played at Welterweight against Burns, Khamzat is also a fighter in the Middleweight class. So Chimaev certainly has a natural weight between Middlewight and LHW. Kamaru Usman has to increase his weight to fight in this class. For me this fight is unpredictable and will likely end in a KO/TKO.I have followed Khabib and Islam social media accounts and it looked they are not way near right now. I am sure that Islam will be with AKA gym guys only in his corner, with the one who helped him to train. Of course Khabib gave him a lot of support during calls, but I dont think he would be around. Because he trust Islam and in 100% sure in him. When Islams opponent was changed, Khabib and Islams team did not care much. Khabib simply told - "Islam is a champ, he must be ready for everyone. If King Kong fits in 170lb, bring him in" 
Without Khabib, I think Islam would have a little difficulty. What Khabib has is the ability to analyze the opponent's gaps and then exploit them to attack with his sambo wrestling. This was very visible when Islam vs Oliveira where Khabib gave advice to Islam several times so that the match ended in a submission. If I pay attention when doing a Takedown, Islam tries to bring his opponent into Khabib's corner to get some advice in the fight. If I'm not mistaken it was like the Islam vs Dan Hooker match where Islam managed to lock him up with a kimura.