it takes some time to get used to the "new/different" early game in FFH, which can determine the rest of your game. Focus on eighter education or mystisicm early on (i prefer education) to get some additional science coming in. Start with a straightforward civ, like the grigori or the bannor, and try to read up a bit before starting a new civ (yes, every single one has different strategies).
Basically, in FFH you need to specialize. Don't aim on being good at everything, pick one route (preferably the one your current civ is best at), and aim on getting the optimum units in that tech line.
About unlearning: Basically look at what cyther said. the metal line isn't everything. While in BTS, your best bet units usually were axemen - swordsmen - macemen (atleast for the core of your army during the relevant period), in FFH you can perfectly build entire armies out of horsemen, recon units (hunters, upgrading to eighter rangers or assassins) or mages. All promotion values in FFH have been doubled, causing experience to weight heavily on a unit's value.
To summarize: forget BTS. The basics are similar, but the way the goals achieved are very different. Start low, and work your way up once you learn the new mechanics. Plan your civ. When starting out, expecially after having played a few games, you should have some idea where you're going with the game, what units you're going to aim for, what religion you're thinking of adopting (major change here: every religion has different effects), etc. Don't expect to learn everything over night, but in the long run you'll find the mod beats regular BTS easily