I'm relatively new too I've been pure CG going on to 2 months or so I think. I recently bought the CG handbook if you're just starting out you might want to pick up a copy it has a lot of helpful information about cleansing styling and trimming curly hair. It even comes with a DVD that shows you how to wash your hair. Best of all it's not expensive here in the USA I got it online at Walmart.com for $10.

As for your questions, yes you can cowash every few days. I usually cowash every 2-3 days depending on how my hair is looking and if I've gone to the gym.

Yes you are correct no brush should touch your hair after you have styled it and it has dried. Only detangle when you cowash and should be done gently.

As for products in the UK sorry I can't help but they have threads on here where you can swap buy or get advice from curlies in the UK.

You should definitely find out your hair properties. Once you know that you'll know what your hair needs and what products you should try. You can find that info on this site. Sleep on a satin pillowcase or wrap your pineapple in a satin cap or scarf to minimize frizz. You can use a mix of water and conditioner to mist your hair after undoing the pineapple to revive curls.

Good luck on your journey and your curls are already nicely formed so they should become spectacular.
curl type: 2c/3a on a good day
med/high porosity & high density
hair strand width: med/coarse
BSL hair & growing