[SelfishGene]

Against the computer AI the most consistant 'startagy' is to hire every mercenary company available, no matter the cost or which company becomes available. Sell gems if short on gold.

Mercs have a twofold benefit. They expand you military much faster than you ever could by simply training them, and most especially they have no upkeep. 100+ normal units can be a heavy load on your monthly payroll, but 100+ mercenaries have no upkeep at all. This more than compensates for the high initial hiring cost.

Mercenaries are always better than the equivalent trainable units because they come with experience and are generally skilled enough not to rout (the barbarian merc company is a notable exception). Also it keeps you away from buying the cheaper, less effective 'crap' troops every nation has at the start of a game; troops which become obsolete rather quickly.

Mercs are also rather cheap to maintain/re-hire as long as your expanding by one or two provinces a turn. In fact i think for most mercenary companies it costs the same or less to hire them a second time than it would to payroll an equivilent number of troops.

During this early phase try to hire few normal troops yourself, except for casters or researchers, to keep expenses down.

Doing this will quickly rack up hundreds of gold in the bank letting you go on a building spree and help strongly consolidate your holdings. By this time many of your merc troops will be depleted by attrition so you can being letting some of their contracts expire and so start to transition to a conventional military.

Against AI. Not vs. other human players. The AI doesn't seem very competitive on bidding for merc contracts on the lower difficulty levels.