1) Please try this solution https://www.8theme.com/topic/modify-single-product-content/ Let me know. 2)
.single-product .tabs .wc-tabs { text-align: left; }
3) Do you mean something like – http://prntscr.com/jhnvsq ? Please describe the desired result in details. 4) Settings > General > Membership > Anyone can register + Theme Options > General > Header Settings > Sign In link position.
Regards
