Margin scheme

I buy and sell rare stamps, and use the VAT Margin Scheme, but am not certain that I am using it correctly.
Most of my purchases are from auction houses in the USA and most sales are to private individuals in the USA.
A large proportion of the lots I buy at auction comprise collections of many individual stamps. I break these collections down into individual stamps (or occasionally groups of related stamps), which I then offer for sale through a certain well-known on-line auction site. A buyer might buy several stamps from me at the same time, and the auction site will combine those purchases onto a single Sales Record.

I usually make a single shipping charge per Sales Record, regardless of how many stamps are involved, how bulky the package is, or what means I use to send it (e.g. Royal Mail tracked/signed for, DHL, UPS, Fedex, …). Inevitably, the predicted shipping charge does not correspond exactly to the actual cost of P&P. Sometimes I make a margin on it, sometimes a loss.
I am now also selling to customers in the EU. For the margin scheme I must generate a Stock Book for all such sales.
1) Should I include this shipping charge within the price received for the stamps, and apportioned across all stamps ?
2) Most payments are received by PayPal – can I allow for that cost (again apportioned across all stamps on the Sales Record according to their sale price) ?

Occasionally I might buy stock from UK auctioneers. Even more occasionally, a lot bought in the UK might have VAT on it.
3) Can I reclaim the VAT on the purchase of this lot (I know I can claim the VAT element of any commission charge) ?
4) If I then sell this lot to a purchaser in the EU, should I add VAT to its sale price ? This is actually infeasible, as the buyer wins the auction for the price bid, regardless of where he/she lives. And if I had to lose the VAT within my selling price it would make me uncompetitive for potential buyers outside the EU.
5) Do I have to generate a Sales Invoice for an EU buyer of an item on which I had to pay VAT at time of purchase ?
6) If this incoming VAT-charged lot comprises several individual stamps, which I then sell separately, but combined with other stamps which had no VAT when purchased, how on earth do I account for VAT ?

I rather hope I’m making this more complicated than it need be. But I fear it might well be worse. Any responses welcome.