ECommerce website using available OS Platforms

I am setting up online store for USA market with more than 10,000 plus products. This may exceed to 30,000 in 1-2 year time. I have done some research on different open source platforms and need help on choosing one of them, its installation and data import which may be provided by suppliers in Excel or CSV format, etc. Following points are need to be considered in finalizing the platform;

a). Cost effective on long term basis; like it should be not very heavy to affect hosting cost, maintenance and troubleshooting cost, etc

b). Have option or flexibility to import and export data in standard formats.

c). Ease of maintaining it without help of expert/developer

d). SEO friendly, payment options, shippoing feature, security measures, etc

e). Other standard / popular features mostly ecommerce websites offers.

f). There are various templates available in market for various platforms. At this stage, I am thinking to use one.

Please do quote the previous relevant work.

Please quote a fix price. If you need further clarifications please do not hesitate to ask.