You can get a seat assignment on intra-Europe LH legs when you check-in for your TATL flight. Only once in multiple trips across the pond have I not been able to get a BP for an LH flight when connecting from UA. Others, on the UA forum, certainly have had more misses than me. You will arrive at T4 and take the bus to T1. There is an LH transfer desk outside the *A lounge to get your BP and there are at least a couple of drinking establishments airside in that duty free vicinity.