Should I mix my own 'mud' (joint compound)? I'm trying to smooth out parts of my wall and also to cover some patched areas.
My "drywall guy" (and the pros on construction sites) uses all pre-mixed compound in buckets.
Green lid for applying tape, blue lid for top coats and spotting screws.
He did say you can get 20 minute or even 5 minute dry mix and he has used these for very small repairs when you want the mud to dry extremely fast. These products have extremely short work times so you really have to know what you are doing.
So, like all things, there are products for specific tasks and the size of your job. Make your choice accordingly.
I would agree with @ArchonOSX if you were a pro. Someone who uses it for a living will use a 5 gallon bucket of joint compound fast enough to prevent storage issues. I have always had issues storing the left overs. By the time I get back to use it, there is dry compound stuck on the edge that falls into the mix. I use the dry mix. I mix enough to use in the designed set time. If I have to stop the work for some unseen issue and it sets up I have only lost a small amount to waste. The rest of the bag can be stored for years.