First of thanks for your honest feedback.
Yea, you are right that we are not native english but we always try our best to do communicate with our customers and clients and give them best supports.
About FontAwesome integration - We don't think its hard to implement, but you should understand that as by default Nioicon used everywhere so you will need to change everywhere manually. But we believed that it may take around 20 to 30 mins to reflect everywhere, just like find replace.
You mentioned that code is not quality and every single files need to review - First of we make the file separated so it can maintain easily or edit/remove easily without reflect others. Also if you ever look bootstrap sass files core code then you will understand why there is lots files as each file serve for a purpose.
Secondly, icon used unicode value on each variable, yea you are right we use as it required. We are not sure if you ever look at fontawesome css codes or any font-face libraries code, but you know they also used unicode to connect icon. But as always you have a readable variable/name that you can easily understand or use.
About other 'libraries' - You said that 'its almost impossible to remove'. We are really not sure how you are using the our template to extend or try to customized but if you using gulp then removing anything takes maximum 10-30 seconds. But if you don't use gulp and work with our pre-built files then it will be bit difficult as it all files compiled where original source available in src/js or src/scss folders. Hopefully you can understand.
Again we are sorry if our english is not clear to you. Also we feel sorry that our code seems very hard for you to understand.
As always if you need any help, please feel free to contact.
Thank you very much.