I wouldn't recommend Hermes - they are shite in our area and parcels never arrive plus their claim system is daylight robbery. I always use Royal Mail and get a Certificate of Posting. If I think an item is going to sell for more than £20 then I will send it 2nd Class Signed For so it is insured. Don't worry if you can't post immediately after a sale. You have the choice of a longer dispatch time when you do the listing.
The Ebay postage calculator is not always accurate and I prefer to use the Royal Mail Get a Price website and weigh each item using my kitchen scales. I add £1 for the bag and packing and I enclose a printed invoice and my address. I bought a pack of plastic mailing bags off Amazon for about £2.75 for 25 bags which are handy.
Always try and end on a weekend evening. You can request a time to end the auction but I think there might be a small fee for that sometimes. I would list your items separately starting at £4.95 as Boden sells quite well. Give measurements as PPs have said. Armpit to armpit garment laid flat, inside leg, length and waist measurement.
I always sell clean washed clothing and state this in the listing. If you are non-smoking household say so as this gives buyers confidence that the item is fresh. Good photos, I find, take a bit of practise but I manage on my phone. Accurate descriptions are a must. If an item is not in good condition say so. If there is some pilling or a tiny mark mention it.
TBH, if a buyer kicks up and wants a refund don't even bother to argue with them just ask them to return tracked (or send them a PrePaid label which you can download on eBay). It took me quite a while to find my way around the eBay website but it has improved enormously and their help centre people are very good.
And good luck! I sold a load of my old clothes that no longer fit me and I have made several hundred quid in just a few months so it's deffo worth doing.
Blimey that was a bit long!