As a guideline, once I get it leveled side to side with the Lynx blocks, I use the stabilizers to put firm pressure on the frame to support it. To achieve some level of consistancy, I use about 1-2 turns of the crank past foot contact. The next day you may have to readjust as things settle.
You can't really use "feel" as accurately because the farther down the stabilizer is cranked, the less feedback resistance you feel at the crank. I have some doubt you can seriously damage a trailer with jack force accidentally, but these stabilizer jacks can put in quite a bit of force if you're determined, so use them within their intended purpose and you should be fine.