itch.io

One newbie friendly strategy is start with Economic hero instead of combat ones, you can get early advantage like 60% discount to all building or Units and extra gold and unit generation 
Than in week 2 or 3 you just buy combat hero and use those extra units to steamroll all neutral stacks and closest enemy AI or at least have powerful enough army to stall until your friend comes to help. Pillar faction seems to be exceptionally good at pulling this off. And they have quite powerful lineup of units.