First, welcome to TPT! And congratulations on researching before setting everything up. My first tank was an impulse buy, more or less, and due to terrible advice from the LFS worker everything was dead in a week.
it is a 48 litre tank... and i would prefer 'real' plants.. so i dont put the carbon in?
No need for carbon in a planted tank, as others have said. If you're having problems with water discoloration at any point, say due to adding driftwood, I recommend purigen instead. It lasts longer, won't remove anything you don't want removed, and can be recharged.
the bio-media is like ceramic tubes (noodles i presume) (+sponge etc) so do i need to mix the ...chemical stuff (can you tell this is all new??) with the water to then wash them in?
Yup, bio-media is usually something like ceramic tubes, or a sponge. It's anything with a lot of surface area that can be colonized by the nitrifying bacteria your aquarium needs.
And by chemical stuff, I assume you mean a product like prime, designed to neutralize chlorine in water. If so, I would just fill up a bucket or some container with water and let it sit for a day. At that point most all of the chlorine will have evaporated, and the water is good to go to use for whatever. It's what I do every week for water changes and maintenance, rather than buying something else to add to my water. Of course, adding prime or whatever is faster.
it says to replace these every 4-8 weeks, can you recommend anything better? (more permanent) and do they need replacing or just 'washing'?
You don't want to replace your bio-media. When you're doing regular filter maintenance, just take it out, rinse it off with aquarium water, or if it's a sponge give it a squeeze and rinse, and put it back in.
Mechanical filtration media, on the other hand, should be replaced around this often. For that I and many others have had great success with plain old polyfill, or pillow stuffing. Just don't use anything with added mold inhibitors or whatever. The stuff is dirt cheap.
And as some tips, as a beginner starting into aquariums, the nitrogen cycle is one of the more important things you're going to want to learn about and understand, if you haven't already. That and never buy a fish on an impulse without knowing what it needs are nuggets that could have saved me a ton of wasted effort and money.
But good luck! Keep coming back with any questions and people on here will be more than happy to keep you informed and help you out.