usually you pay the ap on collection day, a dealer may ask for a deposit for any extras you order. ive just ordered my next car and the ap plus extras less the dealers contribution leaves £448 to pay but not until collection day.
regarding the tracker i would have thought they would have requested it by now if they wanted one. as previously stated by others its usually in cases where the vehicle could be misused by others when the disabled person has less control over its use.