Hello and welcome back. That sounds very traumatic about Marmalade - I'm so sorry. Your new baby hamster is, frankly, too young to be rehomed. At three weeks, it is true they are separated from their Mother but usually remain living with their siblings until about 6 weeks old - which helps them learn socialisation skills.
So it will need some special care and gentleness. He can learn his socialisation with you however, and should be able to be tamed quite easily. But he may be quite scared easily at first, so take it gently.
In terms of a water bottle - if often doesn't show if any water has gone down as they drink such small amounts. The main thing is to make sure he can reach it easily and it's working ok. Did he have a water bottle previously? He is probably using it or you would have seen signs of him failing by now. I am also cautious about using water bowls, especially with such a young hamster, but I know they are popular now. If you use one then it needs to be on a solid surface like a shelf, so it can't get bedding etc in it, perhaps in a corner of a shelf so it can't be knocked over or easily fallen into. And something very small and shallow (like a small tealight holder mentioned). Some tealight holders are actually not small! So it's for the smallest size. But if you're concerned he's not using the bottle then adding one as well might be an idea.
When the hamster is out you could tap your finger over the end of the bottle to show him how to use it.
Harry Hamster is better than the Nuggets. It may be the breeder suggested the nuggets to make sure the hamster gets all the nutrients required, but you'd be fine with Harry Hamster as well but would need to supplement with fresh food as Elusive mentioned,. Their digestive tracts are sensitive at a young age, so if you change over to Harry Hamster it needs to be done gradually - over 2 weeks or more. So maybe just add a little bit of HH with the current food for 2 or 3 days. Then move to a mix of about one third HH and two thirds nuggets for about 3 days - and if all is fine move over to half and half. Keep it half and half for 4 or 5 days and if no diarrhoea then increase to mostly HH with just a few nuggets and after a few days you can give all HH if all is well.
Fresh veg every day and some protein extras like a bit of scrambled egg on a spoon a couple of times a week would be good too.
The main care needed is to avoid stress - a young hamster with a change of environment, if they have too much stress, could develop wet tail. But I think you have everything set up to ensure he will be fine - he has a good cage - but don't clean anything for at least two weeks. I'd say at least three weeks actually - after the first week you could maybe spot clean out a bit of pee'd on substrate if he is peeing in a corner of the cage eg but minimal as you don't want to stress him. I'd say avoiding stress right now is more important than spot cleaning the pee!
Has he made a nest yet?
You'll need to take it at his pace for a bit but he may develop confidence quite quickly. Just keep talking to him gently and offering him the odd treat through the bars. If he starts coming out you could try offering a treat on your hand but only have your hand partway in the cage. If you can get into a routine of feeding at the same time early evening he should start getting up at that time for food. But he is bound to hide away a bit at first.
I would also add a second water bottle somewhere else in the cage so he has a choice and may choose one over the other. The one that comes with the plaza cage isn't great. I use these ones and they have a clip so the bottle can be attached inside the cage and easily lifted out again. They let water out well and don't drip I find and it's always good to have a spare water bottle in case one fails.
But welcome to little Clover! It'll be lovely seeing him - when he's ready! A tip - I turned the volume off on my phone when taking a photo or the click noise can bother them.