Yes, Honor 9N supports OTG. USB OTG or USB On-The-Go is one of the most recent technologies that allows you to connect your pen drives and in some cases hard disks to your smartphones and tablets. It has a cable and through that cable, you can directly view and use your pen drive in your smartphones.
You can also check the complete specs here: Honor 9N
Honestly speaking, fast charging is the most relevant and important feature these days in phones. You can charge your phone fully within munites while you are getting ready to leave your home. No, Nokia 5.1 Plus does not support fast charging.
You can also check the complete comparison here: Nokia 5.1 Plus (Nokia X5)
I would suggest you go for Nokia 8.1 because it has 12+13MP of a dual camera with Optical Image Stabilization
Both these phones have almost the same specifications at a similar price but the Xiaomi Poco X2 seems to be having a better design.
Check Full Comparison Xiaomi Redmi Note 9 Pro vs Xiaomi Poco X2
I will recommend you Redmi Note 5 Pro. Sporting a 5.99-inch IPS LCD display, it comes with a metal case body and has a thin-bezel design. Under the hood, there is a Qualcomm Snapdragon 636 SoC (8 x 1.8GHz) and it is coupled with a 4GB RAM. With 12 MP + 5 MP Dual Primary Cameras you can capture images of 4,000 x 3,000 pixels. Along with the front camera, an LED flash makes sure that you can make video calls at night. It consists of a 4,000mAh Li-Polymer battery which supports quick charging. It is equipped with a wide range of strong features.
You can also check the complete comparison here: Moto G6 vs Xiaomi Redmi Note 5 Pro