You can run your app using any user. WMI must be enabled, but no remote access is needed. So, basically keep the default security settings untouched and everything will be secure and function as required. Some admins like to do stupid things like disable WMI access completely, which is counterproductive because so many programs depends on WMI (including most Microsoft programs).
1- TA_Flags.TA_USER flag will work on their machine?
Yes, but TA_SYSTEM is always preferable. There's less chance for things to get screwed up if the customer stores the activation data on a system level rather than a user level.
3- Only activating WMI service is enough to make limelm run?
Yes.
4- Are you considering to make us able to pass a pointer of file or / byte[] to PDetsFromPath() method?
It won't be in TurboActivate 4.0. We've considered it, but it didn't make the cut. We haven't ruled it out completely, but we don't see enough benefit to add it to the API. Especially considering that TurboActivate.dat is so lightweight and that you can name it anything you want and put it anywhere you want.