First of all, qualification of EB-A is very high, higher than Eb-OR (EB-1B). I will try to answer your question based on my experience on EB-OR.
問題1: 如何說明research position is permanent? Company offer letter will never mention any permanent job.
In my case, our vice president provided a letter saying my position is permanent. You need to ask your company to do this.
問題2: EB-1的6項evidence中一般至少要符合幾項?
At lease 2. my case 符合4 項 (Rewards, Publications, Review other's work, ?(forgot))
問題3: 在公司工作,什麽樣的evidence最能說明international outstanding?
get a recommendation letter from a foreign scholar. My university requires me to get one letter from my boss, and at least one letter from another U.S source, at least one letter from foreign country.
問題4: 如果補材料後,最後還是被deny, 以後是否還可以用OR or NIW?
I think so.