What you are asking for is some smart way to manage queue. Luckily it is already promised in future version.
We are still working as fast as possible on a better system for transfer standby queue management
(quote from the pinned topic)
I think what matters mostly is total number of active peer connections, not a number of seeding torrents. Unfortunately Tixati doesn't have total connections limit, just per transfer limit. In my opinion it would be great to have separate peer connection limits for downloads and seeds.
Torrents with no leeches shouldn't affect your browsing, unless there are many other seeds, which Tixati tries to connect continuously. A few torrents, with hundreds of seeds each, may slow things down. I guess you'll have to limit "concurrent connection attempts" in that case.
From my experience it is best to:
1)
set reasonable outgoing bandwidth limit - this is most important, set it to about 70-80% of maximum outgoing bandwidth, you can also experiment with autolimiter, it is very good tool but not as easy to set as hard limit,
2) set low maximum peer connections limit, 25 is minimum per transfer
3) set lower priority for populated torrents, especially those with many other seeds, give higher priority for rarely downloaded torrents with low seed numbers