That really goes to far off topic. Therefore I've split it into an own topic. 😉
1/ There is no known issue about such for the tracker. He gets reports from over 300 thousands of torrents each 30 minutes, all sorts of torrent clients and user
2/ I've used up to 3 different clients on my computer at the same time (µTorrent, Vuze, qBittorrent), no problem as long as they don't download or seed the same data files. Making them access the same files caused errors.