WebPlus X5: E-commerce Please Help :)

I have a few questions I hope you can help.

1. I have linked my designed site to Paypal but when i select a product to buy in preview it adds it to the cart but if i select something else it removes the item already in there so i can only add 1 thing how can I amend this please?

2. Can i have a fixed cart on the page rather than a floating cart?

3. How can I add a shipping cost Please? the cost will vary depending on the number or weight of items added to the cart

4. Should I be using the Database option?

Sorry I am very confused

Thanks

SM:HELP