Plus one for Ion Auth. And a huge overwhelming plus one for using Bootstrap for the front end. Do not underestimate how much work goes into bootstrap to make it compatible with hundreds of different types of phones, phablets, tablets, screen resolutions, etc. Unless you are working with a team of people dedicated just to the front end its about the only thing that will allow you to build confidently. And if you are starting now, then
go directly to Bootstrap 4 alpha and embrace cards! If you do you will be way ahead. Cards are already here and they will become the dominant layout pattern very quickly.
Otherwise - I think you should do your own system - but with the idea that you are going to release it to the public.
In other words - keep the mindset that you can not put in a bunch of customized personalized shortcut code that only you understand.
Make it as clean, clear and direct as possible. Name your methods well and refactor until they do one thing well. Watch robert martin (uncle bob) clean code lectures on youtube for tips and inspiration.
The problem with a CMS is that it needs mountains of code to accomplish what a few simple templates can do. Anything that tries to automate
the process of building pages and layouts without any actual coding - adds so many complexities that you become a slave to the CMS. The code that it puts out is most probably not going to be very lean. Making changes is much more difficult. Really the only reason to use a CMS is because thats what the client uses and you are getting paid to use it or because you need to work with a large team.
