It all depends on your capacity and the health of the bait--other stuff factors into that like water temp, etc. For example, if you have a four scoop capacity, and the bait is in great shape with 69 degree water, jug that thing! If the bait sucks and the water is warm, maybe just go with a couple scoops...
Buying 4 scoops and putting it in a 2 scoop tank makes no sense at all. So you should approach your thought with these suggestions.
"As much as you can...." means. ...As much as you can fit for the size tank you have.... without over crowding. Over crowding weakens the bait.... killing it. Scales come off.... not enough dissolved oxygen, the problems run on and on.
What type of bait tank.....shape.... fill and drain configuration all are key parts of that decision. Don't want to make it complicated. ... but it's expensive to "kill it" (your "live" bait) before your first stop. Happy to give you an educated suggestion..... but need more details.
All day bait for 4.....are you gonna chum? Live? Dead? 2 Scoops in the 90 gal works unless the weather is rough. Plus in my experience every bait receiver gives a.little different amount. What's cool about 2 separate tanks..... 2 different types of baits. Macks and sardines. ...etc.
Two scoops is better than one but not as good as three assuming your set up can keep them alive.
I like chumming a lot and not having to worry about capacity, but if you are thoughtful (chum a couple of sticks here n there and chunk up the slow lethargic bait instead of tossing it overboard) 2 scoops can get the job done, no problem.
I found you have to chum pretty hard initially to get the YF to come up. Make sure you are on a decent school (lots of marks) before you dump a bunch of bait. After they come up, a couple of sticks here and there along with a steady chunk will usually keep them with the boat.