This - I think dropping the car off at her house while awesome to think about, could easily backfire and be spun as a bit stalkery.
But turning up at arrivals will blow his mind - especially as he thinks that you believe he is coming home on Saturday.
I'd be tempted to just walk up to him, hand him the keys and tell him which carpark the car is in and to expect the divorce papers - no conversation, or other engagement.
However - I'd actually be more tempted to see if it plays out - if you go to arrivals or drop the car off at hers, he will know that you have access to the iPad an will cut off you ability to keep track of his message PDQ.
If you let him come home on Saturday and don't say anything, you will be able to see if he means what he says to the other women about telling you he wants a divorce.
If he doesn't say anything, you can keep tracking his emails and phone messages with the iPad until your solicitor has the documents ready to serve!