Can the UK afford all those F-35s?
The sticker price of the F-35B isn't the real cost to the UK as it manufactures a fairly large part of it. The sticker price of the F-18E/F is what would have to be paid plus the cost of a number of T-45s for training plus the cost of replacing the results of a steady stream of airframe losses during normal use.
The expectation is that if the new carriers were ever full of F-35s then a fair number would have USMC markings.
Can anyone afford those F35's?
Adding EMALS to the UK carriers would only be useful for future naval UAVs. The UK really doesn't want to have to keep pilots current at doing conventional deck landings, it is too expensive and you can't rapidly change the mix of F-35 and helicopters on each carrier.