Hi and thanks for your replies - I will be travelling with two elderly people. We will arrive at Heathrow at 9.30 pm. It's too late for us/them to take Hex to city center, then bus to hotel. It is too strenuous. So we intend to take the bus to Heathrow village and stay overnight in the Heathrow Lodge. The 423 stops right there (or at least near there). Then the next day we will travel back with the same bus (hotel provides free shuttle bus too) to T5, then take HEX to Paddington.

The only question that remains: where to take breakfast... The hotel doesn't have one. But I guess we will just have one back at the Airport...