From what I could see it's 23kgs check in. 7kgs hand luggage within the size limits and one extra small carry on bag free. I assume this last item would just be the sort of small bag you would carry your document's in.
Just did Bangkok to London a couple of weeks ago. Did the electronic check-in which made it easier at the airport. Just had to drop bag off and that was it. As for seat selection I didn't bother as flying alone, and personally not bothered where I sit.