Yes Abraham Lincoln would be a good fit for America and make US more industry and science focused rather than nature and culture. If you played Civ6 there was a great US Civ war scenario so it would be great if they brought that back in another expansion.
Yes definitely but maybe keep the sea dog and redcoat as well as having the Longbowman, or if that was OP maybe drop the sea dog for the new unit. The MOAR units mod already includes the Longbowman and the design is perfect anyway. Like Philip I could just imagine Henry being very passionate and theatrical as well.
Yeah I think that even though I would want to see Isabella in game it would be for all the wrong reasons (or right reasons

) Philip is great already and Spain is one of the best designed and accurately portrayed civs in the game already so if it aint broke don't try and fix it. I agree that they would be very low down on the list of civs that could do with alternate leaders.
Speaking of lists of things low down on lists I wouldn't want to see Portugal included until I see 5 or 6 new civs included beforehand. I say this because there are too many European civs in the game already, and besides Austria/Hungary I'm not keen on Firaxis including anymore. Civs like Mali/ Songhai, Shoshone/ Apache, Iroquois, Ottomans, Byzantines, Cathage, Inca, Morocco and Maya are more essential at this point.
I also think that Brazil are kind of like Portugal in Civ6 anyway. Brazil was a Portuguese colony, Pedro and all of Brazils rulers are probably Portuguese heritage, Brazilians speak Portuguese, The Portuguese Royal family moved their court to Brazil permanently in 1808. I really can't see many differences between these two civs. But who knows you could say the same for Britain and Australia and these civs seem to distinguish themselves from each other easily enough.