Women's clothing are the most problematic items to sell, produce the most complaints. You cannot provide too many pictures or too many measurements. Describe any faults in blunt detail.
auction start/end times
When most people are home from work, so weekday evenings, Sunday mornings. Buy-it-now listing, the end time hardly matters.
buy it now
I like these much better than auctions, but must research carefully the right price. Use advanced search "Sold" listings to see what similar items recently went for. Can revise the price up or down before sale.
reserves
Never to this. Start price = your reserve.
postage costs
I do "Free postage" (total BS name) so no one can complain.
Under £20 regular Royal Mail will cover your loss if the item gets stolen by buyer fails to be delivered. MNers diss MyHermes constantly, but i've not had any trouble with them & they are usually the cheapest courier service that is recorded delivery.
You didn't mention minimising fees: very important.
Most Ebay listings end up being for free, you shouldn't pay for the listing; if you see a listing charge, you ticked an expensive box that you need to untick.
Ebay & Paypal together take 13.5% + 20p. make sure your start or BIN price gets you a profit plus covers the your delivery charge, and 14% that is hived off by Ebay+Paypal.