Understanding BIP 143 [hash computation, lockTime, sequence number, witness format]
I believe you can use either at this stage. The marker and the flag show let the client decipher which scheme is being used and interpret appropriately.
lockTime sets when the transaction is valid from. 0x00 is from the first block, 0x11 is from a later block. You can continue to use 0x00 if you wish. https://bitcoin.org/en/glossary/locktime. Most transactions are published with a locktime in the past so that they are immediately mined.
The sequence number: https://bitcoin.org/en/glossary/sequence-number
The stack items depend on the type of transaction. See the examples in bip 141. For example the witness for p2WPKH nested in BIP16 P2SH is "signature" "pubkey"