Powers of Straw Hats:

Luffy: Major haki is color of observation (mantra easier to say and Luffy fight multiple strong guys could chop of his arms if he is not aware of them).
Minor is color armaments (since it is should block Luffy's DF ability also when used so he can only use it just before impact), king's deposition is kinda special since it best used against multiple fodder characters.

Nami: new world weather, better use of her own weapon.

Zoro Major haki is color of armaments and mantra not too far behind.

Sanji Major haki is mostly color of armaments (Luffy and Zoro can easy demolish a building) so while Zoro and Luffy use color of armaments offensively Sanji need to use both offensive and defensive since Sanji usually takes damage straight on.

Usopp: Major haki is mostly(only) mantra since he usually uses special ammo for each job (now he get seeds to trap or eat opponent) maybe he gets some seastones later.

Chopper: I don't think he learn haki so it mostly make friends with local life and better control of his monster mode, better piles that last longer.

Brook: more songs? Brook's DF is most unpredictable one (maybe communicate with ghosts)

Franky: Gundam

Robin: Mantra, knowledge of political system of new world islands

New crew member(s): Hancock , i don't think she will handle of Luffy going to New World without her after not seeing him for 2 years maybe Jimbei also joins, it would be interesting to see how Nami will get used to him

If Hancock joins Luffy i don't think WG will lunch Buster Call as Seastone bottom make them hard to see for Sea Kings but not invisible and if they start shooting it will attract them and if you kill one more will come to feed on it so in the end some Sea Kings will try to eat Marine ships. So it come to sacrificing ships vs punishing Hancock.

Even if Luffy said he needs about 10 it doesn't mean precisely ten member it could be 9 or 10 or 11 or 12.