Shari'ah is for the earthly realm, not the hereafter.

From narrations, we can understand that, in heaven, people will appear in an ideal form (for instance, at the prime of their life, no injuries).

Probably, people will appear in clothing styles that they are comfortable with and which reflect their nature and how they are used to appearing on earth. So for some people this may resemble hijab. Of course, in very nice fabrics and made of materials such as silk and silver (according to the Qur'an!).

This is apart from the narration saying that Fatima al-Zahra (A) will appear while hidden, although this can also be understood to be a veiling of her high spiritual nature that none can perceive, just as none can gaze directly at Allah's power, rather than a basic covering of the body for material reasons.

I am not aware of any restriction presented in narrations on interacting with people at the same level of paradise or below, although we might choose to interact with some people and not others based again on our preferences and expectations.

The immediate resurrection will be naked.