I'll try to address some of the specifics for you.
Part of this is your inexperience - so let me explain a couple of things.
Puppies are like babies. There is NOTHING in the rules (as in been in mom's belly for a couple of months and I've been with all my siblings for a while with mom) that has ever told this pup to sleep at night NOT during the day!
It takes them a LONG time before they sleep completely thru the night. He'll have to potty every few hours for a long time so someone needs to get up with him. You take him out (ON leash -- don't just let him wander - you need to be in control of him so he doesn't get in the habit of going outside just to PLAY at night), walk him in a circle for a few minutes and go back inside. No playing, just 'business'.
Then you go right back in the house to your bed, go to sleep.
That's the theory. You don't let him whine and let him out. nope -- let him out when he whines and you reinforce the whining.
I like their crate up on the level with the bed when they are tiny -- he'll be happier if he can 'see' you and smell you and YOU can stick your fingers in and say 'shhhhh' and keep him happier than he will be alone.
GRADUALLY you get him to sleep longer ... when he gets up and rattles around you say "shhhh" and try to get him to settle in again ... but if he won't you get up and take him out, bring him in, put him back in the crate and roll over. he whines? "shhhhhh" whines some more? "SHHHhhhh" but you don't let him out.
I like a wire crate -- then if he becomes a royal p.i.t.a. I can COVER the crate. (denial of your presence is a subtle but clear clue to him you aren't happy)
Most of the time a puppy has four gears
wake up? PEE ... POOP (err? outside first??? REALLY????? wow!! whatta concept!)
inside ...
EAT .... YUM ...
PEE .... POOP .... (you learn to let him out **immediately** after eating and drinking)
PLAY PLAY PLAY PLAY PLAY
PLAY PLAY PLAY PLAY PLAY
PLAY PLAY PLAY PLAY PLAY
PLAY PLAY PLAY PLAY PLAY
PLAY PLAY PLAY PLAY PLAY
PLAY PLAY PLAY PLAY PLAY
PLAY PLAY PLAY PLAY PLAY
zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz
(that's four -- pee/poop, eat/drink, play, zzzzzzzzzzzzzzz)
In about 45 minute cycles they play and zzzzzzzzz with a little pee/poop and eat/drink thrown in to vary it!!
Generally they sleep little more than half an hour to 45 minutes at first. Then they PLAY HARD often ... playing brainlessly until they crash. zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz
Add food .... then they might sleep and then PLAY *****REALLY HARD*****. But you need to get them *outside* right after the food part so they can elminate and then PLAY.
They'll need to pee/poop after they wake up, after they eat, and ... after they play ... if for some reason they don't finish the pee/poop part because they get distracted **by** play ... well, then you can always stop one of the above to pee or poop!! (that's in the puppy rule book -- trust me -- it's at the top of every page!! LOL)
My serious point is -- you need to take him to potty EVERY time after he eats, EVERY time after he wakes up and EVERY time after he breaks from playing. Or as near to that as you can.
Pups truly need to not make any decisions on their own -- if they decide when to eat ... they're gonna decide when they want to poop and you don't want that. They also are not always good judges of when they should eat and shouldn't.
If you free feed (which is what you're doing by leaving the bowl down) you miss out on a lot of valuable bonding time AND valuable information about your dog. If you never know exactly how much the dog eats (and if you have two dogs you won't know who is eating whose food -- and a pup needs specific nutrition and the older dog does *not* need puppy food).
The pup needs to eat at certain intervals to keep up his blood sugar -- and he shouldn't be gorging at the wrong times. Give him too much food he will sleep too long and then be too hungry at other times. He may associate the discomfort of eating too much and then be reluctant to eat at other times. So even it out for him and TELL *him* how much he's allowed to eat by simply giving him the portion.
That actually may elminate the on/off appetite.
Many dogs don't have a good internal sensor to tell them when to stop eating -- and particularly not puppies.
Now -- the other thing I'm not hearing you say is that he plays and frankly, I would be UBER concerned about a pup that isn't zooming periodically and playing hard. Pups generally aren't happy just being held all the time -- they should*NOT* be actually -- they should be playing and zooming and just ... well, doing SOMEthing ... even if it's ... er ... wrong.
Now ... after they have played, chewed on a toy or whatever they are doing that is 'play' then they will zonk asleep. But it's like that four gears -- wake up -- poop/pee, play, eat/drink, poop/pee, maybe play and then zzzzzz, then repeat from the beginning all day.
Does he drink EVERY time he pees? Is his pee almost odorless and colorless? That should concern you -- a pup drinking to excess could be a sick pup.
If this pup is truly lethargic -- if he isn't balancing having the zoomies with sleeping, then VET ... now.
Play HARD with him in the late evening and walk him with lots short walks late in the evening (don't make a puppy walk for long long miles long walks -- they aren't strong enough yet) but that will help him sleep.
But it takes a good long while (and several months usually) for him to truly learn to sleep thru the night. And even then, honestly, it's not that they stay awake during the day - they just get stronger. But the periods of napping lessen (and they get stronger and should play longer and longer and HARDER even as they mature).
But developing a nighttime sleep habit is just that -- HABIT. They learn to adapt to our sleep schedule -- it's not that it's really all that natural -- it's just what they do to live with us.