To answer your question:
It depends on your all time highest average upload rate. Each 20 KBytes/s it is incremented by 1.
Further explanations on that number:
It is to be considered when you upload your own new torrent only. It is no longer a rule, it is rather a recommendation. The limit to only one new at a time has been relieved as well. Here the new rule:
"5. Upload only ONE NEW TORRENT AT A TIME in order to initially seed your upload as fast as possible. If multiple torrents are uploaded, they MUST be completed within 24 hours."
This means if you ensure all new torrents to be completely uploaded in 24 hours, you can upload multiple at the same time. A single new torrent can take longer. This is to allow uploader with smaller upload rates to upload (bigger torrents), too.
When no own new torrent is uploaded, there is no limit in the number of uploading torrents.
The number of downloading torrents depends at any time on your upload, share ratio and user status as indicated in the "Downloading Rules".
Low ratio warned users are limited to one download at a time.
Users with download rights suspended can still download a Freeleech torrent.