I ran to it in th morning. Takes a couple of hours to get to top. But there are a few summits. So you can choose where to stop.

That's correct- no charge. The only expense is getting to the trailhead. Yes, do wear proper footwear, and remember you are not in a race!

I went after dark and was very happy about that. The hike to the viewpoints was only around 15 minutes, but it's all stairs and did sweat a lot, even without any sunshine. Descending was no problem because the stairs are very well lit

Ground might be wet. Just be careful

There are no opening times/entrance fees, you can go anytime, a headlight -as mentioned in earlier posts- is for sure a good idea for dark times.

Yes it is.

地下鉄の終点、象山駅が最寄りです。 走ったらすぐでしたが徒歩15分位だと思います。色んな散策道が取れますが、また登山口から戻りました。

Yes true, that there are lots of mosquitoes and that ca be circumvented by liberally using mosquito repellent. Please also note that there are no lights can if you have good bright torches then it can give an excellent view of Taipei. However, if you want to enjoy the various trails (please note that it is not just one way route up and down and there are few other trails that you can explore once you are up there. But at night it may be not advisable to explore the other trails. But if you are keen to just climb up and see Taipei at night it is fine. Also, please note if you are keen to see Taipei at night the other two view points are: 1. Off course 101 observatory 2. Get down via the Maokong Gondola (as it closes only at 9 pm and 10 pm on Fridays, the day before a national holiday and on Saturday and national holidays). It is lovely to see Taipei from that height and the travel time is pretty long at 20-25 minutes so you can really enjoy that ride Have a great climb