My arduino setup does (or will do) most of those things.
The iAqua setup from AnotherHobby does most of those things also, and there are at least a dozen other arduino/raspberry pi setups on this site. Most primarily control the lights, but several do other things also.
In my experience, your arduino can do almost anything. Writing the user interface for it takes more time for me than anything else. Also you have to figure out hardware solutions, and many of the things you've mentioned already have good controllers available, so taking many hours of your time to create your own controller isn't always practical, unless its something that you just want to do.
The one thing I wish my setup could do is have internet connectivity. Being able to control it from a smartphone or webapp would be really cool, but I'm not good enough at software to pull that sort of thing off.
There's a couple good aquarium controllers on the market that are PC or tablet based. They're not cheap, but if you're looking for that much control, it can be worth the money.
Just to give you a ballpark, just writing the graphical interface on my arduino setup for a 4.3" touchscreen took at least 100 hours. Designing, wiring, and troubleshooting the hardware probably took another 100 hours. Not something for the faint at heart.
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