Actually human grade vitamin capsules/tablets aren't really suitable for dogs, especially young pups, so I would definitely recommend not to make that mistake
Buy only vitamins that are MADE for dogs, it was designed for that purpose as dogs' intestines are quite different to humans', humans can take a tablet and it slowly dissolves in their tummy, whereas with dogs, the tablets are useless as it just passes out in their stool, doesn't have time to dissolve slowly.
Too many vitamin tablets over a long period will probably do more harm than good, so just stick with the good feed, a couple of dog vitamin powder and you'll be right as rain.
PUPS under the age of 4mths NEED to be fed 3 times a day. Morning, lunch and dinner.
They can eat up to 1kg meat per day, as they grow they need a lot of energy. 500gm meat with soaked kibble in morning or at lunch, (you can choose whether you want to feed milk/weetbix in morning or at lunchtime) plus another 500gm meat with soaked kibble in evening. Just use common sense when you see how much the pup is eating, when it gets a bit full, take the food bowl away and have a look at how much meat is left, then you'll work out how much you should give the pup each time. As the pup gets older you can gradually increase the meat amount.
I know the same novice trainer who only fed his pup once a day, and the poor pup just looked very lean, with big wrists that had outgrown its body, wasn't getting enough nutrition to match its energy needs. Pups have to look like they're well covered in the ribs (not chubby fat though) and be round, with sparkly eyes, healthy gum colour, clean ears, trimmed toenails, full of boundless energy (if a pup spends all day inside dozing, then it's not being fed right).
You need to give a pup at least 200gms kibble twice a day. With at least 500gms meat twice a day. You wouldn't guess a little pup could eat that much, but believe me, they do.
Cheerio