How many to junk?

Only if you frequently switch mon just before fainting. If you have to revive them as well, might as well use a hyper potion since the revive also restores a portion of their health.

I rarely ever need max potions, that may be do to not having legendareies, and always hyper potioning blissey after revive, but i'd say pitch some max potions, they arent usefull

if this were gen VII where hyper potions only heal 120, i'd pitch them, but since they're 200 HP, dont.

Why would you toss the max potions when you could get rid of all your hyper potions instead? 1 max potion takes up just as much inventory space as 1 hyper potion, but heals for more, making it more valuable.

(FWIW I keep 300 max potions and 200 max revives in my inventory and recycle all other battle items that I get.)

Toss all the hyper potions and 150 of the revives to start. Why hoard so much?
For comparison, here is my bag, I delete Max potions and revives to stay at 120 maximum, I might reduce that to a round 100 soon.

Max potion = hyper potion. As others have said, it depends on your play style, do you switch out, or let them faint? Also, how many raids do you do per day? Apply that play style to revives. I never keep more than 50 revives, as they are easy to get. I have 100 max revives for backup.

Throw the hypers and regular revives. I have only 800 bag spaces, so I limit my hypers and revives to below 20. If need be, I discard all of them, although I usually throw regular balls and razzes first. Max pots and super revives are used only for emergencies.

Gifts do not count towards bag space.

This gonna make some battle addict to be jealous in old gym system
Now, not so much, unless you are willing to spend money on raid passes amd have a small group of trainers to do that..

Buy more bag space!!
Just kidding, I agree with others, trash revives and hyperpotions, and perhaps most of your max potion too, depending on if you raid/attack a lot. Opening 20 gifts per day will refill your supply of good items quickly, as will spinning stops to get gifts to return!