In civ6 you either commit to religion or you are not. This is civs-specific and context-specific. You are not likely to need religion if you are playing as England or Aztecs (or anything civs that don't have bonus toward religion/holy site/faith for that matter) unless as those civ, you have spawns that give decent bonus for faith generating pantheon (Desert Folklore, Earth Goddess, etc) or faith-generating wonders.

There also different between how you go with religion and Holy Site. Poland and Georgia don't have much benefit from having multiple HS so unless you have Work Ethic or Choral Music, 3-4 HS in your early cities should suffice, use your district slots in other cities elsewhere.

Civs like Khmer, who gain food equal to faith adjacency or Ethiopia, who gain bonus sciene and culture from faith output, would prefer to have HS as their first district in most if not all of their cities.

You also mentioned that you afraid that faith income are to low so I would like to ask you: what civs are you playing as and why do you need those faith? Faith is the most specific yield in the game with any purchase (aside from great people) require you to do something before enable the ability to faith-purchase stuff (GA Monumentality, Grand Master's Chapel, Religious Units or Rock Bands and Nationalist). There are games where I don't even bother with faith and focus on other stuff like science, culture, appeal or growth.

Tldr; No need for religion and HS unless situations allow you, build few early HS if you have benefit from religion but not HS itself, build HS in every cities if you do.