On one hand I love the situations you suggest, the possibilities for creative play. On the other hand I want to have henchmen and hirelings be a significant part of this campaign. Your multiple attacks will be your henchmen. If I allow multiple attacks I worry about handling time and having 15+ minute battles like later editions.
Later editions have 1-2 hour combats. 15 minutes is nothing. Don't fear the second action.
I guess part of it will depend on what level those henchmen are. If they are around level 1-2, they will die of quickly in battles with 5+ level pcs and monsters. If you have a bunch of 5th+ level hench men then yes, battle would start to noticible slow, I would imagen, espicially if you have alot of them. If you only have one or two henchmen, I think it will be ok. If you have a henchman for every party member, and double a party of 5 to 10 by adding henchmen, and then having to add more monsters to balanch out the encounter, then you have longer times playing out combats but its probably more to having a ton of hench men to keep track of more then the extra attack.
If you wan't that many henchmen, you can either let each pc manage each henchmen and thus the game will not slow two much. If you want to manage all those guys from behind the screen, I would say standardized them so they all roll the same action dice, with the same bonuses, and the same weapon damage and damage bonus, as well as let them all have the same hps and AC in order to stram line the process. YOu could also take away the henchmen's extra action dice, but let the players, who are the real heros any way, keep their extra action dice. This will also help keep the henchmen from stealing the players thunder (which not to many players like), while providing meat for the grinder to instill fear and/or a sense of revenge in the player characters.
Play test it out and see how it goes. you can allways drop those extra action dice after the fact if you and your players decide it dose slow down the game without adding to it.