Can't help with the transport question, I'm afraid, as I've never been to Croydon.
The checklist should be a) on the application form and b) exactly the same as the fiancé visa except that instead of sending proof of contact and plans to marry you include your marriage certificate and evidence of living together. Also, no sponsor letter is required as you will be there in person to answer any questions.
All other documents should be the same as the fiancé visa and should be all prepared and ready to go by now
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