Apologies for this delayed reply; it took me a while to realize what you were getting at with your shipping description. I'll address that after I answer your other inquiries first.
You can prevent overselling out of stock items by using our Inventory Control feature:
http://www.e-junkie.com/ej/help.inventory.htm
You may want to combine that with our Variants feature for products like T-shirts that have options such as size, color, etc., so you could assign each specific Variant its own inventory stock quantity under a single product:
http://www.e-junkie.com/ej/help.variants.htm
Once you set up your products in E-junkie Seller Admin, we provide you with ready-made HTML codes for your E-junkie cart buttons, so you would simply copy the codes from us and paste them into the HTML source of your own Web site pages, wherever you want our buttons to appear among your own layout, text and images. This page explains our requirements to integrate PayPal with your E-junkie cart:
http://www.e-junkie.com/ej/selling-with-paypal.htm
(Note: do NOT use the "PayPal Cart" button codes available in Admin; these no longer work properly due to changes at PayPal's end which we have been unable to work around, so they will be removed from the next version of Admin. The standard E-junkie shopping cart button codes will offer buyers a PayPal checkout button in the E-junkie cart).
If the shipping categories you described are based on the order weight or item subtotal (pre-tax/-shipping order total), you could set up Shipping Rules like this:
Go to Seller Admin > Cart Shipping Settings and set up the following:
Shipping Origin: Netherlands (enter any 5-digit number for zipcode, as that is a required field but only applies to US origins);
Shipping Destinations: if you will only ship to certain countries, select them in the list, or otherwise select nothing for Worldwide shipping;
Leave all other settings blank or 0.00;
Click Next to save settings and proceed to the Shipping Rules screen.
In the Existing Shipping Rules menu, select and Delete any Rules you may have saved there. Add new Shipping Rules as explained below -- any settings not explicitly instructed here should be left blank or 0.
Set up your first Shipping Rule for Domestic shipping:
Shipping Rate Calculator: Flat
Shipping Amount: 3.00
Country: Netherlands;
Max. Weight OR Max. Item Total: (use one or the other to set the largest order this Rule will apply to)
Click Submit to save the Rule.
Next Shipping Rule for Domestic shipping:
Shipping Rate Calculator: Flat
Shipping Amount: 7.00
Country: Netherlands;
Min. Weight OR Min. Item Total: (use one or the other to set the smallest order this Rule will apply to)
Click Submit to save the Rule.
Those examples should give you the basic idea how to create Rules; for the middle rates you mentioned, you would set both a Min. and Max. threshold. You would need to set up Rules for each European country, then you can cover the "rest of the world" by setting up Rules that apply to All Countries (which really means "all countries in your Shipping Destinations list that don't have specific Rules of their own").
Once you've set up all your Rules, click Back to Admin.
Then, whenever you add or edit a product's settings:
On the first screen, if Shipping/Buyer's Address is not checked there, tick that box;
Click Next until you reach the Shipping Options screen;
- Weight: enter a weight if you'd set up weight-based Rules, otherwise leave blank;
- Package type & Capacity won't matter here.
Click Next until you can Submit to save settings;
Repeat this for all your tangible goods;
When adding new shippable products, remember to enable Shipping/Buyer's Address.
