Improvised weapons are usually left to the DM. There is very little we can tell you for sure. Most of these questions have to be asked of your DM.
Improvised weapon as melee and ranged weapon
A weapon can be considered both a melee weapon and a ranged weapon. many throwing weapons do that. An improvised weapon could also be – you can hit someone on the head or throw a rock at someone, and both would be attacks with an improvised weapon. On the other hand, we can imagine a thrown game card being able to hurt somebody, and it's hard to imagine how you can melee someone with a map that hurts you. (It probably does not count to hit her only with the card wrapped around her fist.) Your DM may or may not allow it, but it probably depends on whether you can imagine it actually hurt anyone.
Melee weapon mastery and ranged weapon mastery with throwing weapons
In any case, thrown weapons, if allowed, can be both melee weapons and ranged weapons, and the phrase for melee weapon and ranged weapon control means that you get the bonus if you use the right type of weapon, regardless of the type of weapon of attack you do. And officially they are stacking. So you could get +4 to attack with a throwing weapon and cause damage if you have both. However, you should ask your DM for it, as it may be cheesy for some DMs to get both. Personally, given that you've burned four exploits this way, I do not consider this a very good option, even if your DM allows it – weapon focus, weapon specialization, melee weapon control, and ranged weapon control are rather poor exploits.
Magic improvised weapons
To become magical, a weapon must first be a master weapon. An improvised weapon is by definition something that is not a weapon at all. If you made a card that was designed as a weapon and of masterful quality, it would no longer be improvised, but a real weapon. Whether this is possible or not in your game world depends on your DM.
Ask your DM for fancy, perhaps exotic weapons that are actually weapon-laden playing cards. Maybe polished metal edges. Maybe use the stats for a dagger. Then you can get masterwork versions and magic them, and there are no questions. To have indeed Impromptu weapons are a bad idea – there is really no advantage in using them at all, I have tested.
Also, you probably should not take Weapon Focus unless something really good requires it. You probably should not take four levels of fighters – one level of power per level for the first two levels is fine, a level of performance that's really weak on every second level. And even if you do, you almost certainly should not choose weapon specialization. That does not bother the Weapon Mastery exploits, but they're not that good anyway. Instead, I recommend a look into the masterpiece of Complete the Warrior, Bloodstorm Blade Tome of the battle is also good for throwing. If you want to be force-based, choose Brutal Throw from Complete the adventurer is good and the Ranger can use you to skilllessly engage in dueling or ranged attacks. If you want to be based on skill, then Dead Eye by dragons Compendium Dex can damage you, and if you treat the cards as if they were daggers, Shadow Blade will use them Tome of the battle will also (they stack). Swordfighting is useful for keeping the Shadowblade, and there may be more useful things you can do as well.