Can Cs-Cart do this?

i dont know about the multi-vendor, your last question, but :

Yes, it allows/ handles searchable custom field for products

yes, you can create where when you buy one thing then go on to next. you will have to read the manual to learn how to do all this though.

I set up a multi-vendor ebooks store. I paid for a custom addon to do this. As CS-Cart for a quote.