Dean,
you will have rather detailed description of Anglo-Russian landing and French invasion in Mathieu Dumas (see link) :
Court of Naples did not declare war to France in October 1805, as I erroneously wrote, but "indignantly" left anglo-russian land at Naples on 20th of November 1805.
Russian General Lascy and his assistant general Hopperman was preparing the invasion of Italy from Naples since 6 month (May1805), reconnoitering Neapolitan frontier.
2.000 Albanians were part of Russian expeditionary force, just before French invasion of 1805 (Russia could easily recruit Albanian mercenaries, from its basis in Ionian islands). Which could explain that Albanians garrisoned Amantea in 1806, if they just changed master when Joseph was nominated king of Naples.
Until anglo-russian landing, French forces were concentrated in Northern Italy against Austrians, and Eugene could supplement them by heavily using Garde Nationale to garrison northern places and send reinforcement of regular units to Gouvion Saint-Cyr, who had just defeated Rohan's Austrians around Venice.
Additional informations from "France Militaire" :
Order to evacuate Naples was sent "just after treaty of Presbourg" (26 December 1805) and before british evacuation of Naples (which could be easier to find in regiment history).
British evacuation was at the latest before 23rd of January, when Bourbons, with no allies left, fled Naples to Palermo.
see "Annual register of world events 1805" :