The LCG faq says:

"(v.1) Deckbuilding Clarifications

A player's three domain cards do not count toward his deck's 50-card minimum."

This would seem to imply a 53 card minimum? Is this true even though LCG doesn't have specific domain cards (we just discard from 8 to 5)?

i think its more to do with domains arent really part of the deck but rather an important part of the game. like the story deck or some way to keep track of successes.

i don't believe it is speaking about the three you take from your hand and place in your domain. It is talking about the 3 cards that you place face down to mark where your domains are. So, you have a deck of 50 cards + 3 cards that are not part of your deck that you place facedown as place markers (where you put the 3 cards that you discard at the start of the game to fill your domains). thos three cards cannot enter play and are not more a part of your deck than the cthulhu markers or the game board. Make sense?

You have it right: the deck you play is at least 50 cards. Then three separate cards face down to be domain. I know this for sure because in addition to the LCG box set I had some of the Eldritch edition boxes, and they contain three domain cards, both sides printed with 'back' patterns.