Thank you both for this!
Just to share - we spoke with a driver and he does not seem keen with Cingjing, especially staying a night at Cingjing. He seems to suggest that it is rather costly to stay at Cingjing; traffic can be heavy; not much night activity (unlike Taichung); temperature will get cold at night (10+ degree C) which might be a problem for my little one (3 yo).
Also for the strawberry farm visit, he also told us it is the beginning of the season and the strawberry fruit might not be fully grown/ready for picking. In another words, we might be disappointed with the strawberry farm visit. (BTW, we will be in TW during the first weekend of Dec 2019). Maybe we'll switch to Xinfeng farm? I read that the fruit season is ending in Dec, not sure if there are any left for us then...

This is the revised draft plan, with some input from the driver:
Day 1 - Taoyuan (late afternoon), stay at XMD
Day 2 - Head to Leofoo Theme Park, stay at Taichung
Day 3 - Xinfeng farm / Lavender cottage / Puli town (paper mill, 18 c chocolate), stay at Lu-Shan
Day 4 - Head to Green Green Grassland, skywalk etc, head back to XMD (after lunch)
Day 5 - Jiufen, Shifen
Day 6 - Taipei free
Day 7 - Taipei free
Day 8 - Go home