You can travel as this is really not an issue at this early stage. You may be placed in Secondary Inspection if you are utilizing your I-751 extension letter in conjunction with your existing green card. The extension letter allows you to travel until there is a final determination/adjudication of your joint application. In so far as being re-interviewed or not its usually a 6-10 ratio, with 4 out of 10 applicants being re-interviewed and usually this also depends on whether you applied jointly or alone (waiver), submitted a lot of documentary joint-cohabitation evidence or not. Often times as the other colleagues pointed out if you filed jointly but did not include to much proof of joint cohabitation, USCIS usually will issue an RFE-Request for Additional Evidence and ask for more. Good luck.