some questions

I assume you are talking about the Fou cards that raise Hp and Atk? If so I would just use them on whoever you like now, they aren't terribly rare and don't give a huge buff. Personally I just use them on whoever I'm powering at the time of whatever class they match.

Friend point summons are not worth saving when you are new. Basically you are rolling for 3* servants that are going to make up the meat of your teams for a while. The Friend points never get banners, the only changes it ever has is that during events they can sometimes get low rarity event bonuses from it. For now though I would suggest friend points be spent freely.

As far as saving SQ its up to you. early on it MIGHT be worth it just summoning off of story or whatever banners are available in hope of getting a few more five stars to help carry you before you really save up, but that's a matter of opinion. Focusing on the 3* units from the friend point summon and saving SQ for good banners should work just fine.

TL;DR Only SQ is really important. Everything else is minor or common so spend it freely.

the cards that give +hp and attack are worth using on your berserker, they drop easy from friend points and events so more dmg hp helps. FP ( friend points ) are uncommon if you don't have any rare/good servant you get 1 free roll a day so always do that.

don't spend quarts as F2P till you look at other sites an found all upcoming servants pick one an /pray that you get em it's 1% chance. i got few 5 stars but i spent money, also if i was F2P i mit still have 1-2 but would been fewer.

try the summon simulator on this site do it till you get 5 * then check what it cost reset repeat that 3-4 times to get a idea of what it like trying pull 1 random 5 star.