1) No they don't. Each class has their own individual free stats to add

2) Yes, you can only use cross class skills from the few classes designated only for Dragoon such as Marauder and Pugilist.

3) Requires some market study, selling raw materials, DoH items all also can give you a fair amount of gil. But to try to make 1 million gil in an instant, that probably is not going to be possible through market. There are many ways to make gil, try to find out