JR Kyushu Rail Pass

Good morning!

I am planning to purchase 1x (5 day) Northern Kyushu Area Pass and 1x (5 day) All Kyushu Area Pass because I will explore Kyushu for 10-11 days. Under the FAQs at the JR Kyushu website, it states that we can purchase more than one JR Kyushu Rail Pass as long as the valid periods of the multiple passes we purchase does not overlap.

I will only use 4 days out of 5 days for the Northern Kyushu Area Pass then I will activate my All Kyushu Area Pass the next day (the 5th day of my Northern Kyushu Area Pass). Will this be a problem if I use my second pass?

Also, on the day I am travelling from Yufuin to Miyazaki, will I incur extra charges if I were to use my Northern Kyushu Area Pass since Miyazaki is outside of the covered area for the pass? Thanks so much!