Upkeep is possible to implement, the important one is finding good upkeep/cost ratio and in my experiences with upkeep, it works best with 5%-10%. For example infantry cost is 2 and 0.1 upkeep (5%) would work perfectly. But armour upkeep should be definitely higher than 5% but still should not be higher than 10%.
Yes, draw means nobody wins and nobody lose pretty much same with chess. Because of the cumulative aspects of games, the loser side really cannot turn the tide of the war and the fate of the games always seales in the middle of games and just there should have been draw option that gives a good reason the loser side to continue.