YES!!! It looks like you’ve got it figured out now. Do all your CSS work in your own style sheets. On a typical project, I may have 5-10 different stylesheets, some of which are only loaded on certain pages because they style components that are only on those pages. Getting comfortable with creating your own CSS stylesheets, and writing your own CSS classes and rules, and applying them through the attributes panel is one of the things that makes this program so powerful.
You’re not limited to staying with Bootstrap’s “look and feel.” You can make your site look and work however you want by writing your own Custom CSS, and as long as you don’t change the name, any Bootstrap class you copy from the Styles Tab into your custom CSS file will override the Bootstrap styling. In this way, you have total control to make Bootstrap “look” and work however you want.
For example, I don’t always follow the Bootstrap breakpoints, either. Sometimes I will even use max-width in my media queries when I want particular things to behave a particular way on mobile devices or very large screens. Bootstrap uses 1200px as their cutoff for XL. Nowadays, 1920px by 1080px monitors are the most popular size. Sometimes I will used a fluid container (so content spans the full width of the screen, but limit the max width on a row to 1600px. Things like that.
I’m going to sleep now, but I’ll be around and working most of the day Saturday from about 2pm (Eastern Standard Time) until 11-12pm at night. That’s my “9-10 hr productivity zone”, so if you get stuck, that’s when I’ll be available.