It will be released mid April, but will be available at Salute. Armies? Carolingian Frank, Old Saxon, Wend (Slavs), Gascon/Basque, Emirate of Cordoba, Lombards, Avars and a Thematic Byzantine expeditionary force.
You can take an elephant for each 250 points of the army as a whole, but due to the 20% allies limit you will get a maximum of two since two elephants and a minimum size light cavalry unit cost 183 points.
Yes the list says the Illyricani are formed, evading cavalry and the Sagitarii may be skirmishers. You could indeed use the Dark Age cavalry as you suggest, you might want to replace the spears with javelins but it wouldn't matter too much.
It is option 3. The exit point is that at which the centre of the unit left the table. The entry point of the centre of the unit is anywhere within the normal move distance of the unit along the table edge, measured from the exit point. The unit makes a normal move from the entry point in the remain...
There are no mounted troops using crossbows, to my knowledge, only light crossbows.
If a Dark Age army with crossbows fights a medieval one with crossbows, both should use the same rule, which one I don't mind.