1) Wilayatul Faqih means that in the ghaybat of the Imam (as), a mujtahid has some of the functions that are required in a Muslim society such as right of distribution of inheritance, marriage and divorce rights, and so on.
2) Marja is followed in Fiqh rules. It is everyone’s own responsibility to research their aqidah and make sure it is correct therefore that is unrelated to the matter of taqlid.
3) The rules of following a marja are mentioned in the beginning of the risalah of all the maraje and are almost identical.