While I'm sure Fantasy Craft will have feats, and possibly advanced actions or tricks (although the AAs and tricks may be in a PDF or Signs & Portents) to help support this, lets see what we can do with what's out now.
hands-on: how can you guide your mount with your knees so to have your hands free an shoot a horsebow? is it a stunt? if yes, what DC?
There aren't any rules to cover no-handing a HDO check, looking at the tag description and the Hands Free upgrade in Fragile Minds
I'd likely house rule it that a normal horse (or whatever ) can't be controlled with just the knees and make the following NPC Quality available:War Trained (+2 XP - mounts only, 'trained')
The animal is trained as a war mount and to respond to vocal and tactile directions in addition to normal control cues. A mount with this training allows a rider to make one handed Manuver checks at no penalty and hands free Maneuver checks with a -4 penalty. Additionally a rider with the One Hand on the Wheel feat may make hands free Maneuver checks at no penalty.
This hack will work for now, and I'm confident FC will either have something like it, or more likely a slicker solution, especially as the guys have been leaking that mounted combat isn't quite like vehicle combat.
fighting in melee combat form a horseback qualifies as: crowded, tight..?
Almost certainly tight, but the Chase rules may not be the best choice for mounted combat that isn't, well, a chase. Most vehicular combat falls into the chase DC well, but normal mounted combat doesn't really. That's why the FC book is supposed to have additional mounted combat rules.
it costs me one half-action to move my mount at full speed (+5 to DC) and then i still can make an atk. without a malus?
The only rules we really have at the moment for mounted combat is the Chase DC which can be run alongside combat. Under that a rider needs to spend one half action to make a Survival/Manuever check which would allow him to move the mount's full move and then has one half action left for fighting.
do i understad this right that mounted combat is completely skill bound and that i don't need extra feets? (Like mounted combat an mounted archery in D&D)
It's not completely skill bound as most of the Chase feats are just as useful to a horseman as to a driver, but the most crucial thing for mounted combat (without seeing Fantasy Craft's rules) is the Survival/Maneuver check.
And , as a bonus:Horse, war (Animal — 79 XP):
Init IV; Atk V; Def VII; Resilience VI; Damage Save: VIII; Skills: Notice III; SZ L; Spd 50 ft; Qualities: attack on command, fearless
(Large), improved scent, inferior attribute
(Cha 6), low-light vision, mount, natural attack
(kick III, trample III), superior attribute
(Str 14, Dex 13, Con 15, Wis 12), war trained