BPM Process Set Human Activities to user's groups

BPM Process Set Human Activities to user's groups

  
Hi all,
I have a few questions related to the activities's assignment to groups of users.
First of all, if the customer don't want to use the EPA TaskBox and have more than 1000 groups synchronized with AD, what is the best way (best-practice) to do this with our custom task box/list?
I know that we have the API BPMActivity_SetGroup, but related to this I have some doubts. As I can see, we should have EM groups related to our groups and we have to maintain this synchronism (no problem), however I suppose we have to have also N permission areas for different groups and also maintain this dynamically, because the number of groups and their elements will be highly variable.
Another concern and doubt is the performance..With such a number of permission areas, performance will not be affected?
My last question is, when we open an activity with an user of a group (the one linked to the activity), the activity will be available for all the other users in the group or not? In the negative way, how can we enable that feature?
Hope someone can help me on this.

Best Regards,
GM