Hi Brunov!
let me reply in your questions:
1. add multiple products into a cart or do I need to buy them separately
Answer: Shopping cart is coded at the moment, will be in the next update (which is free)
2. offer a donwloadable item upon a specific purchase amount
Answer: You can use "bundle" feature for this I think. Once someone buys one of your expensive items, he can access the bundled bonus content.
3. have limited qty of one product to download. (eg only the first 25 are able to get it)
Answer: Yes you can.
4. specify a different qty of available download per product category (mp3/ebooks) or per customers groups (affiliate/registered/new/non registered)
Answer: No
5. generate a direct download link that I can send in my newsletters (to offer a product to my subscribers)
Answer: That's being added too in the next update.
Total list of upcoming features:
1. Shopping cart.
2. QR Fingerprinting of PDF documents (adds qr code to footer pages, once scanned see he user id and email of the buyer, and the site he downloaded from)
3. When generating order for a customer to allow email and direct download link delivery.
Let me know if you have more questions!