From my experience, a torrent doesn't stay without seeders for long once it is made freeleech

Indeed… I regularly make torrents such as Terence Davies freeleech when I'm the last seeder left, and I have enough bandwidth to most leechers' capacity, yet the majority of data is downloaded from other users (total snatches 300, my own ratio 100; leechers uploaded twice as much as me). This is a good thing if you like to spare bandwidth or to accelerate downloads; less good if your objective is to increase your ratio.

At the very least, you must ensure that your upload bandwidth has capacity to upload the entire torrent ONCE during the freeleech time. In the worst case, all leechers will be stuck at the same level until the very end, your ratio for that torrent increases by 1 and they all swap their respective chunks until completion. If you are tight on bandwidth and/or you are the only seeder, you might want to add a comment and specify that in your calculations the speed will be sufficient for everyone to complete download.

If the member who is making it freeleech is one of the seeder (best the only) and sure to have a good enough upload rate to seed it completely in a short time (best much shorter than 24 hours), it can be a plan to increase the share ratio. A member described that plan somewhere. Personally, I find the plan a little risky in terms of ratio.

If the member who makes it freeleech is not one of the seeder, there is a certain risk that the upload of a full copy within the freeleech time isn't achieved. This risk increases with less seeder and bigger file size. IMHO, five seeder should be enough. Even one seeder can be enough, if he got a good available upload rate. Most seeder here have their torrents seeding without uploading much data, because of missing downloader. So even with few seeder in most cases their nearly complete upload rate will be available, especially as torrent clients give priority to torrents with low seeder to leecher ratio. So for an average size torrent with 1 to 2 GB file size, even one seeder should be enough.