The habitual present is used to indicate the frequency something happens. Thus, with regards to your examples:
1: Do you go? This would be acceptable only with prior context, otherwise I do not know what is being asked about. It would only be habitual present if the prior context was along the lines of "The gym hosts aerobics classes every Friday." (even then it's debatable). There is no temporality (time) indicator.
2: Same explanation as above. Note that don't is a contraction of do not and phrases like "do not you go?" are awkward sounding so using don't is correct when contracting but 'do you not go?' would be more natural if not contracting.
3: The comma is unneeded here. This is habitual present.
4: Correct and habitual present.
So yes, habitual present is about adding temporality indicators such as today, always, often, and so on.