the multy action penalty for attacks and defense actions are tracked together, but you get one of each without penalty. So if your character is being attacked by three ruffians who got the drop on him your defenses would be at -0, -2, and -4; but when it comes time to counter attack (if you survive) your first attack would be unpenalized, but if you made a second attack it would be at -6. note however that all of these are for melee only. in ranged combat your options are attack or defend, once you've fired in a round you don't generally get the option to dodge as well.

for handweapon skills if you have a close skill you suffer a penalty based on how different it is to your skill. so if you have handweapon: swords, and you are using a knife, you would probably suffer a -2 penalty while using that skill. (the exception is the huge knife/ short sword these can be used with either skill equally well)
If on theother hand you have hand weapon: polearms as your closest weapon skill to a dagger you are going to suffer at least a -4 penalty to that skill.

and in the case of improvised weapons if you break off a table leg and have hand weapon clubs or staves then you would probably not suffer a penalty to hit with it, but it would not be as reliable of a weapon. (and most likely the balance would be off) also using a broken bottle with the hand weapon knife skill would probably not suffer a penalty to attack, but you'd have a hard time parrying with it.