> I'm a software engineer with a full-time job, but I have lots of spare time in my off hours. I'd like to monetize this time
> I'm not looking for massive pay, just something to occupy my time and some side money.
This opinion will change. I 100% guarantee it. A few years ago, I had the exact same reasoning for starting freelancing on the side. I even justified my desire for more paid work as "I'd be programming on personal things anyway."
So, I took a freelance job. I thought it'd take about 6mo of weekend work. And I took it at 40% of my normal day-job rate because, it was "friend" work, and, again, "I'd be programming anyway."
It took two years.
That was two years of nights and weekends that did not belong to me. Two years of not being able to devote time to exploring other technologies, learning new things, or just goofing off. I took vacations from my day job to work on my side project because I was so desperate to get it done and have freedom again.
The opportunity costs involved are absolutely massive and should be heavily weighed before deciding to take on more work.