Questions regarding Hinduism

Hello there, I'm new to Sanatana Dharma is having a date or girlfriend a sin ? What Hinduism says about premarital sex and sex in generally ? Also, I'm from Greece and we don't have Hindu temple here. Can I still do a puja even without going on a temple ? Finally, what about figures like Babas and Sadhus ? Can I still chant their mantras (loke Sai Baba of Shirdi) ?