Shopping Cart Plugin

Hey guys… there seems to be a few shopping cart plugins that could be possible, and since I dont want to make a mistake with this part (wont exactly be like a typo you can jus edit on the web page!) I need advice on the best cart plugin for me. Here are my priorities:

1. Has to be SEO friendly – which I am sure most are, but this is a top priority
2. Must be able to support multiple upsells on each item… i.e., just imagine a suit sold that can also include a belt, a vest, hat, etc. for more $$$. I may have up to 20 products (for now) at once time available for sale, and each product will have possibly about 20 upsells attached to them.
3. Should be scalable – this is not THAT important since if this is needed, that means I will be able to afford to pay someone else to upgrade my cart for me, but I would rather, with everything else being equal, start with a cart that does not limit me to a certain amount of inventory or be so fragile with “heavy” use that I will be forced to upgrade no matter what very soon.
4. Being a web designer, I dont need the CMS portion so easy to use, but if it is easy to upload and manipulate products + images + videos possibly, it would save me a ton of time and will be easier for me to train someone to do it later.

I really hope most of you agree on one, not like 2-3! Thanks guys!!!