I start with the default Bootstrap design and tweak it was I go by overiding the defaults. Initially I will change the primary color. This will give you a decen

I start with the default Bootstrap design and tweak it was I go by overiding the defaults. Initially I will change the primary color. This will give you a decent font and basic elements. No need to buy a theme. They come with tons of extras which you won't use and will make it harder for you to make edits. On the front-end side, React feels like the most popular JS right now and appears to be widely used. It has an extensive eco-system. Vue.js is popular but is mainly a one-man-band. If you are doing this to use in a work environment, I would go with React. Else go with whatever you prefer.