Well, I am not an expert from the switch end of things, but I can answer some of your questions.
One DSL per subscriber.
Each DSL can, at least in theory, support up to 8 terminals. Not sure how this correlates exactly to TSPs, and most switches do not support 8 terminals.
In reality, in the USA, 2 wire is used from the switch to the prem and 4 wires is used from the network termination unit (NT1) to the terminal. However many terminals support 2 wires with the NT1 internal. In most cases those device cannot share a DSL with another terminal
(unless they are clever and break out the 4 wire outsid ethe terminal. In that case a 2 wire terminal's NT1 could be shared with up to 7 other 4-wire terminals)
One and only one NT1 per 2 wire circuit.
Up to 8 terminals (at least in theory) can share the 4-wire circuit.
2 Wire good for up to 18k ft.
4-wire good to a maximum of 1 kft (best case, with several limiations.
Each DSL includes 2 DS0s ("B-channel") and can therefore support 2 simultaneous circuit switched calls.
Each DS0 can support circuit switched voice, circuit switched data, or both types of calls.
Terminals may support 1 or 2 B channel operation.
Nortel switches support "DMS Custom" and/or "National ISDN-1" and/or "National ISDN-2" D channel protocol. Not all terminals support all available protocols.
I hope this helps :)
TIP: If you ask a better question, you will get a better reply. Be specific so we can help!