I developed eye floaters about a year ago that are annoyingly noticeable against any page with a white background. The Dark Reader extension (https://darkreader.org/) has been a life saver for me, and I've found my eyes to be less tired overall when using it, too.
My only wish now is for a way to invert PDF colors on Mac - I haven't found a good way to do that short of inverting all screen colors, which messes up all the other apps that do have a dark/night mode.
I would have my retinas checked by a retina specialist. Floaters may indicate retina issues that may lead to retina detachment. If caught early there are better options for remedy.
Try to focus on one specific technology that is popular in enterprise software and become an expert at it. Take one to three months if possible and just focus on that one thing. I'll use the example of front end development with Angular. Watch a bunch of youtube videos on it and read the docs. Set up a free github account and set up a free github pages blog and do deep dive blog posts on angular topics as you learn and also build demo apps that demonstrate your mastery of specific angular best practices. Put that stuff on your resume and present yourself as an expert on the topic. Side opportunities may open up as well. As an example see how this guy has set himself up as a django expert: wsvincent.com
One of the more difficult parts of self hosting with a service like digital ocean is managing your own database. Luckily DO just introduced managed postgres databases. Also you can use DO load balancer so you don't have to manage a load balancer and deal with setting up let's encrypt ssl certs, and only have to worry about deploying your web app. I wouldn't go with docker for production just yet because while docker is great for immutable servers and dev/ops parity, it makes things like secret management, logging and monitoring more complicated.
Don't know about books but you might check out thegreatcourses.com that has many videos that try to explain math concepts in a simplified manner by lectures from college professors
One good middle ground option may be installing and running your language/framework locally but running supporting data services such as mysql, redis etc in docker containers.
Laravel even more then rails and django comes with pretty much everything you need for modern web dev built in. Full auth system, feature and unit test infrastructure, background jobs, push notifications integrated with a scalable third party websocket service, integrated with vuejs, webpack wrapper and more. It also has a prebuilt development VM that has supporting services such as mysql and redis or you can use various docker solutions for that. There is also excellent laracasts video course platform with free series on getting started with laravel and there is also codecourse video casts that has examples of full blown websites built with laravel
The method I like to use is to intertwine MVP development and customer feedback together as I incrementally build an MVP. So you should start with identifying your target customer and get them involved in the building of the MVP from day one.
Ask yourself WHY the real live person you have identified to sell your product to would want to use your product. Then find out if that is really true by directly telling them this is WHY they should use it and monitoring their real response of either paying you to use it or not. If they don't then you need to find out why and adjust.
My only wish now is for a way to invert PDF colors on Mac - I haven't found a good way to do that short of inverting all screen colors, which messes up all the other apps that do have a dark/night mode.