As to whether a foreigner can follow something Indian or not. To clarify this, I will quote from the Yajurveda. I specifically take the Veda, since there is an opinion that one can receive initiation only in Tantrism, the Bhakti or the Nātha traditions, but not in the Vedic one, etc. Here is a śloka from the Śukla Yajurveda (Vājasaneyī Saṃhitā), from which follows that there is no absolute radicalism towards foreigners even in Vedism:
यथे॒मां वाचं॑ कल्या॒णीमा॒वदा॑नि॒ जने॑भ्यः।
ब्र॑ह्मराज॒न्या॑भ्याँ शू॒द्राय॒ चार्या॑य च॒ स्वाय॒ चार॑णाय। (यजु ० २६। २)
I have transmitted the auspicious words of the Vedas for people like brāhmaṇas, for kṣatriyas, vaiśyas, śūdras and for araṇāyas (foreigners).