Technically, transaction amount is of mutez type, which is internally represented by 64-bit signed integer.
However, in practice, (if we speak about applied transactions) the amount cannot exceed the total supply, wich is currently 873682204744114 (https://api.tzkt.io/v1/statistics/current).
And yes, a single transaction can have only one destination address....
I suspect you mean amount as transaction size and not as a mutez value.
The limits per transaction and block can be found in the following RPC: /chains/main/blocks/head/context/constants