hi, my ebay acc name is donnamiggsy and i have over 1000 feedback and have used ebay lots.
here are your answers---
1) if you want £20 for an item, i found starting the bidding at £19.99 is cheaper than setting a reserve as a reserve usually costs £3 upwards. to list at £19.9 would prob cost 20-25p....
2) ebay charges 10% - if it sells at £20 your fees are £2 etc...
3) weigh the item and log onto royalmail website to see how much the postage is for that weight. i usually add 250g for the packaging weight. beware though that some catogries have postage limits, if its gona cost more click in top right of page to change forms to more options, where it states postage in listing put heavy/bulky items and put postage costs in listing or just put item to collection only and put postage costs in listings. if you need to alter invoice, click send invoice and just alter the postal service and put cost and click send.
4) yes anything you sell will automatically go into your paypal as long as you enter the address at the bottom of the page where it asks for it.