ecommerce with specific functionality or requirements

I have a few clients asking for ecommerce websites and each has their own unique need:

1. One client has over 1,000 or so products within about 10 categories. They need a platform that has a unique search filter for each category. So category A searches on 4 fields while category B searches on 4 different fields.

2. One client sells a few different products but each product can come in a number of sizes. I want to find an ecommerce platform that will allow me to build a page for each product. Somewhere on the page I want to have a table. In each row it would be the different sizes of that product. The columns would have a few fields and then I want it to have a text field box for the quantity the user wants to order and an add to cart button. This add to cart button can either be the last column or at the bottom of the table.

Basically, I want to allow a user to order multiple sizes from a particular product on one page.

I know this is definitely possible, but just need to know what platforms I can do this on. I have been looking for an example of this but can't find one that is exactly what i want (but that is probabyl because I don't know the right industry or website to look for).

3. One client wants to allow users to purchase registration to conference or training sessions online. Each would have a set date & time and # of seats available for that session.

4. One client already has a website but now wants to sell a few products (less than 5) but wants a simple shopping cart and not just individual links to paypal or such.

I know that I am asking alot in one post but I figured it was better to do it in one thread than to start 4 different ones.

I appreciate any advice and recommendations that you guys have on these situations.

 

Thanks