Sorry I never got back with these answers:
1. Which word appears three times in a row in Tanach (there are a few answers, 2 of which have a slight change)?
2. Which two words appear 3 times consecutively in Tanach?
1. ayc was right with Kadosh, Kadosh, Kadosh (Yishayahu 6:3), but also Ava Ava Ava Asimena (Yechezkel 21:32). The following two have slight changes in their structure “Eretz Eretz Aretz (Yirmiyahu 22:29) and M’dinah M’dinah UM’dinah (Esther 8:9)
2. Heichal Hashem, Heichal Hashem, Heichal Hashem (Yirmiyahu 7:4)