You can't choose the inputs but you can choose the addresses in your wallet from which coins will be used. All the outputs sent to those addresses will be used.
Yes you can. First select the addresses you want to send from.
Then, in the send tab you will see a list of transaction outputs, and you can remove the ones you don't want to send from.
To send to multiple outputs, just type several lines in the payto field, with a comma separating the address and amount:
screenshot:
https://electrum.orain.org/wiki/File:Electrum_multiple_outputs.pngand of course you can combine both: select inputs and send to many outputs
