A Muslim is allowed to perform any number of optional Tawafs. While doing so, he or she need not follow it up with Sa`i. While doing the optional Tawaf, it is best to complete the full seven rounds. However, if one is simply doing an optional Tawaf, there is nothing wrong if one discontinues without finishing the total count.
Sheikh Ahmad Kutty, a senior lecturer and Islamic scholar at the Islamic Institute of Toronto, Ontario, Canada, states the following: There are different forms of Tawaf. Besides Tawafs that are part and parcel of Hajj or `Umrah, some of which are either obligatory or recommended, there is another type of Tawaf that is considered as supererogatory or optional: It is comparable to nafl or supererogatory Prayers. Just as we perform two rak`ahs of tahiyyah (Prayer of greeting) while entering a mosque, likewise we perform Tawaf as a form of greeting while entering Al-Masjid Al-Haram. Moreover, just as we are allowed to perform any number of nafl Prayers any time other than during the forbidden times, likewise, we are allowed to perform any number of optional Tawafs. While doing so, we need not follow it up with Sa`i.
Finally, while doing the optional Tawaf, it is best that you complete the full seven rounds. However, if you are simply doing an optional Tawaf, there is nothing wrong if you discontinue without finishing the total count. It is analogous to praying nafl; ideally, while praying a nafl salah one should do two rak`ahs. But as Caliph `Umar (may Allah be pleased with him) said, when once he simply prayed a single rak`ah and said “salam ” and was asked about it, it is simply a nafl, so one is free to do as much as he or she wishes to do.