Nobody can say you how many story points can you take for your first sprint. First of all story point is unitless value. You should not make initial decissions like 1 story point = 6 hours because in many cases it will trun against you later on. Also each project can have different "size" of story points.
Commitment should be done based on Planning meeting with product owner. You will go through user stories and PO will explain some details about them. She will also provide some acceptance criteria (definition of done). Planning meeting is time bounded (based on sprint length and size of the team) so the first observation is how many user stories you were able to discuss. Based on the information received from the PO the team shoud be able to make professional judgement of how many of discussed user stories can be done in the sprint. Because the team knows that it is initial sprint and nothing is done yet, the team will probably commit only to a small amout of work but this will increase in future sprints.
Pure story points value should not be used for planning and time estimatting. It should be used to describe relative complexity but still 8 storypoints can mean something between 6-12 (fibonacci) story points in reality so saying that 8 storypoints equals to 4 days is really dangerous because it can be also 3 or 6 + "waste" (overhead) in initial sprint.
One of the main agile tenets is Empower people. Planning and commitment is exactly that empowerment you give to the team. Team is responsible for delivering commited user stories but of course they can fail and they mustn't be blamed for commitment failure in initial sprints. Initial sprints are for calibration.