Just some quick suggestions; writing a service that uses xml or json is just as easy as using email, but it's a more marketable skill these days (I don't remember if you had a real software job already or if this was just a hobby). Since you have a real front end, the users won't care either way.
Second, and this is less of a quick suggestion and more of a design suggestion, go real time. If it's a multiplayer game, one action per week is going to be kinda boring. Go real time and support scheduling of actions. Here's an example:
Player 1 has three or four slaves/monsters. He logs in on Sunday morning before church and sees that his npc's weekly action points have reset, so he decides that he'll put the girls in training for today (-x action points), have one fight tomorrow while the others watch (-y action points for the one, -z for the other two (with a tiny xp bonus for watching fights)), then he'll continue to schedule actions for as long as he feels like it (up to several months in advance if you want). If the game sees that his actions are possible, it accepts the schedules and will require no further input unless something happens to make the schedule invalid (a girl gets impregnated and trades ownership, a girl gets killed or seriously injured in a fight, loses the ability to fight via being crippled, etc). If a schedule is invalidated, an email can be generated to alert that player, or he can just find out the next time he fires up the client. Girls with invalid schedules can just default to something sensible if the player can't update them (rest to recover in cases of injury, in cases of pregnancy/change of ownership the player can't have any input for her anyway).
The point of this suggestion is that it allows players to be as lazy as they want, logging in very infrequently without punishing them, while allowing more active players to be as hands on as they want (scheduling per day, for example) without rewarding them with anything other than fun and slightly more optimal results (say they look at the arena schedule, see a girl they know they would like a shot at owning, so they pick one of their girls who can probably beat her and schedule a fight at the same time hoping they get paired up).
So, yeah, the scheduling thing and having the program do results once per day might be more annoying to write than once per week, but I think it's more rewarding for players to be able to pick how active they want to be. And as it's a suggestion, I won't be offended if you tell me to go fuck myself
Edit: Another benefit of allowing long schedules is that it will make it easier to seed the game with "NPC players" when starting out to make sure all players have enough opponents in gladiator matches, while letting it eventually become all real players once there are enough to keep it going.
