list packets output & other misc

[shmick at riseup.net]

in a test key i have 4 subkeys; 2 for sign and 2 for encrypt

gnupg automatically chooses the most recently created 's' and 'e'
subkeys to sign and encrypt a file

how can i mandatorily specify using other subkeys for the same primary
key for 's' or 'e' either on command line or in an email client for
example ?

when i list packets, it tells me which key was used for 's' (in long
format) but for 'e' (in short format) it says gpg: encrypted with ELG
key, ID 0x00000000

how do i determine which key was used for encrypt ?
do i assume it used the most recently created 'e' subkey ?

is there a reference for the numerical values of version, hash, cipher,
algo, sk2, etc ?