Getting started with Wordpress theme development

I'm just getting started with Wordpress theme development. I was able to put together a very crude theme- it would not be 100% usable, I just made it for learning purposes. My next step is to investigate what goes into making professional quality themes. Below are some questions.

1. 
   

   What frameworks are recommended? I used nothing but bootstrap, are there recommended PHP or MVC frameworks I should consider? - also is Subime Text 3 a sufficient editor for this?

   
   


2. 
   

   Is theme development a one person job, or do good themes really require a small team?

   
   


3. 
   

   What things should be considered in order to map out a plan or architecture for a theme?

   
   


4. 
   

   Any advice on how to position yourself for a career making CMS themes and plugins? I'm currently designing websites using already made themes and modifying the php in some cases for added functionality - but I would like to make my own themes instead. I have a degree in computer science so I think this should possible eventually.

   
   

I would very much appreciate any pointers or advice!