A more open layout is actually a good idea while the rats are still settling in, so this is actually a great first setup. This helps the rats acclimatise to their new home more quickly; a layout with a lot of cover and enclosed spaces would allow them to hide away more, which means they can take longer getting used to their new environment. In fact, if they seem at all nervy, I'd suggest removing the couple of enclosed houses you've got in there at the moment. If you have any flat hammocks, those would be great replacements.
If those wooden shelves are uncoated, you may wish to remove them and coat them with a child-safe paint before putting them back in. Most rats love peeing on flat surfaces for some reason, and untreated wood will just soak up the urine. Plastikote enamel is a good option for coating wooden platforms, though it can take a few coats to get a wipe-clean finish. Alternatively, just leave them out and replace with rope toys or smaller perches. I do like putting platforms in when I've got old or infirm rats with mobility problems as it helps a lot with safe and accessible layouts, but hopefully that won't be relevant to you for a long while yet.
I can't tell exactly how deep the base is, but if you can manage to put down some loose substrate at the bottom, that will be great both for more digging opportunities and also smell control. For the cage base, most people use chopped cardboard or good quality (dust extracted, kiln dried) shavings, usually ones marketed for horses (!). The bales are huge but they last ages so it's actually much cheaper in the long run than buying rodent substrates, and since horses are sensitive creatures, their substrates are generally much better quality too.
The shredded paper in the trays at the moment is great for nesting and foraging, but it's very low absorbency so it'll get smelly fast, especially if the rats use them as litter trays. Paper litter pellets are the best choice for litter trays as they're much more absorbent, but still safe if eaten (which rats will sometimes do...). Breeder Celect or Back 2 Nature are the leading brands of paper-based litter; they're made by the same company and almost identical so people generally use whatever is cheaper, and there's a few other places doing paper litter as well.
The wheel in there is too small for adult rats, but fine for youngsters, so feel free to leave it in there until they grow out of it. A 30cm/12" wheel is the minimum for adults, though larger girls and most boys will find that too small. Tic Tac wheels do 14" and 16" metal wheels; I'd just save up for one of those if you can. (14" should be fine for all girls and smaller boys, but when I upgraded to a 16" I noticed my larger girls suddenly doing a lot more running. So I just advocate going for the biggest one regardless of sex and size now.
) The plastic 12" wheels (Silent Spinner and Wodent Wheels are the two main ones I know of) are cheaper, but Silent Spinners in particular have a tendency to break, so once you've had to buy a replacement you may as well have saved for a Tic Tac. Wodent Wheels don't break that I know of, but they are very noisy and a real pain to clean.
One last thing: the Pets At Home nuggets aren't great for rats. A few well-respected breeders noticed the incidence of mammary tumours increasing sharply when they incorporated PAH nuggets into their rat mixes, and then dropping off again when they took the nuggets out. So I'd suggest switching them off it ASAP. If you want something you can buy easily at a shop, Reggie Rat is actually not that bad. You can scatter their dry food in the trays of shredded paper too, instead of using a bowl, to make feeding time more interesting for them. You can use the bowl for water instead; some rats prefer drinking from a bowl, and many rats enjoy having a bit of a wash in one.
Longer term, a lot of people get their food from Rat Rations: https://ratrations.co.uk/
There's a lot on the shop so don't panic while you get lost in there.
You can make it as complicated or as simple as you like; to keep it simple, go for one of the Isa-Mixes (under Complete Mixtures For Rats), and supplement with some DailyRat3 stuck to some wet food like lightly oiled veg a couple times a week (under Health and Treatments). Rat Rations also sell a variety of substrates so you can get some from there to make best use of the postage.
Sorry for the essay; I know there's a lot to take in.
There's a lot of articles on rat care here if you want more info: viewforum.php?f=11