You've done a great job so far! When I started knitting, my piece would've holes in my work just like yours. I would mindlessly pick up stitches in between 2 stitches and I caught that mistake early on, thankfully!
To answer your questions, I didn't have an issue with stitches falling off so I didn't purchase any stoppers. If I were resting my work for a bit, I'd scrunch it down to the bottom of my needles.
Secondly, I learnt the knit and purl stitch at the same time and played with those two for a while to understand the difference.
Thirdly, it took me the making of a simple beanie to completion to get comfortable with knit and purl stitches.
Fourthly, depending on your interests in knitting, you could get circular needles (to work 'in the round' as well as 'work flat') because you can work on enormous projects on those needles. They are definitely an investment.
Lastly, I have a vague understanding of how knitting works. Atleast enough for me to be comfortable with it haha
RE: Learning to Knit One Stitch At a Time