Welcome to the guitar! The problems you are describing are very common frustrations among beginners, so don’t worry - you're definitely not alone!

As far as nylon vs. steel, I’d stick with the sound you love the most at this time. Getting your fingers in just the right spot in the Spider Legs exercise is a journey - something you will continue to hone over time. Even if you are not landing it spot on at this point, the exercise is still really good for developing hand strength, coordination, and orientation.

consider the tone and placement issues to be a work in progress.

the way you describe it, it sounds like you’d want to work on getting as much of a top-down tippy-tippy-tip of your fingertips point of contact as possible. Hitting adjacent strings is often caused by the finger coming in at a bit of a angle, which can often be tweaked and improved with attention and intention and practice.

Have fun! - Lisa