Hi Gary,
I’ve no experience with foreign contactless cards. My understanding is that most will work.
On charging, yes you will only get one transaction per day. However, if your stay is for more than a couple of days then you might be better off using the Oyster and adding one topup to cover the several days caps. You can topup at the ticket machines at Heathrow so I don’t think the queues should be too long. If they are then maybe use the contactless card for the one journey into Central London and then top up the Oyster there.
If you can give me a few more details about the trip (dates, likely destinations/zones used, etc) I should be able to suggest an amount to add. Also please confirm whether it is a normal blue Oyster or a visitor Oyster card.