Questions on creating open source theme option framework?

Hello,

I am trying to develop theme options framework like “Redux Framework” but 100% open source and I wanted to ask for some help just on 3 things that I have some doubts on the basics, that are the following:

1) To create option on admin panel on the right menu bar this needs to be done with plugins “Advanced Custom Fields Pro” and “Custom Post Type UI” or is recommended to do it some other way? if so which one?

2) To create and option on framework like for example “changing background color” is this done by calling functions on wordpress or this has to be code from scratch? or what way you recommend?

3) Is there any developing license I need to get on plugis to develop this? If so, which one?

Any help is appreciate, thanks!