Welcome from Portsmouth. My advice is because I've made the mistakes already is to not be fooled into buying really expensive gear because of good marketing and flashy photographs. For example, I bought an £80 pair of Montane hiking trousers and I later bought a £7.99 pair of walking trousers from Decathlon, the Decathlon ones are MUCH, MUCH better!!!
My hiking underwear is great, boxer shorts from Decathlon, lovely fit, £3.99 a pair! A great pair of soft warm gloves from Decathlon, £1.49.
I'm not specifically pushing Decathlon, just highlighting that good things can be bought cheaply!