Wanting to try pressurized co2 but some problems

It wont hurt to run an airstone at night. Are you planning on running the co2 for 24 hours? Best bet is to get a regulator with a solenoid to shut off at night.

You will need to spend a little time getting it adjusted correctly to attain the levels you want. A good dual-stage regulator will ensure you don't have an end of tank dump problem. Just don't go cheap on the regulator and even a single stage can work for you just fine. You can also employ a ph controller which will shut off the CO2 once you reach a target ph. Ph lowers when you add CO2.

I don't think you will have issue. I always check on my systems, near daily but not really needed. I have never considered them set and forget though. With a few safeguards in place you will be okay.

the system im getting thats used comes with a 5lb tank and a milwaukee ma957

Those regulators are not the most reliable and well known issues with end of tank dump. I had two of them. One did the end of tank dump and killed the 10 fish that were in that tank. It is not to say that you can't use it, but if you really are worried about the fish in that tank I would suggest you control its operation with a ph controller. Or, ditch it and get yourself a dual stage.

Yeah prob the best xase scenario

Or you can do what hundreds of folks do! Just refill the tank before it gets anywhere near empty. Even with the world's worst reg, end of tank dump will only occur at or near the end of tank. Cheap and easy might be to keep a second tank of gas on hand. When the needle begins to go down, swap the tank. The meter won't show any change until all the liquid is used from the tank, so when it starts to move, you got a day of so to notice.