I think I didn't do a good job of explaining myself, when I said relatively "passive"  I didn't mean a truly passive source of income but something that doesn't require a lot of time and pays accordingly.

Maintaining a large number of rigs can be a full-time job but with the monitoring and automation tools that are available maintaining <10 rigs doesn't take that much time, depending on how you set it up.
And I don't want to get involved with anything related to gambling but thank you anyway.

What are some relatively low risk and less time consuming ways to increase crypto holdings? I'm going to uni next year so the bulk of my time and energy this year will be spent on trying to get into a good uni and I won't be able to spend as much time researching coins and studying the market. I'm currently looking into mining and arbitrage trading bots.

I have decent experience with mining equipment and there's also the advantage of living somewhere where electricity costs $0.025/kwh (and I'm currently in the process of trying to get a place with $0.007/kwh) but after running through some rough numbers it doesn't look like you'll end up with much more cryptocurrency than you started with unless you buy second hand hardware or go asic. (Asics aren't that accessible where I live amd are usually sold at a significant markup)

Another thing that crossed my mind was setting up a very small miner hosting service, is that something people would even consider? A few mining rigs, if setup well, won't require a lot of time to maintain with enough know how and I can provide significantly lower power and maintenance rates than most large scale mining colocation/ hosting services but I'm not sure on how to prove credibility and get the client to trust me.

I'm also looking into writing a simple arbitrage trading bot but it's still just an idea that I need to spend more time developing and I'm also not that comfortable with keeping money on exchanges for long periods.

Any advice or constructive input would be greatly appreciated.