You think you can train yourself for 20 hrs?
Instrument flying is a skill set that may very well one day save your life….or end it.

You use a sim to be taught and practice things that are either too dangerous to do in the airplane such as unusual attitude recovery and various instrument failures in “actual instrument conditions”.
Practice approaches that are not available in the vicinity of your training airport such as a back course ILS or NDB approaches.
Yes you should still practice them.
In addition you can save a lot of flying around time by rapid repositioning for another approach with different wind and turbulence conditions. Something that you can’t do in real life. If your home airport has an ILS you can do about 3 in an hour. With the same conditions obviously. In a sim you could do 6 in the same amount of time with changing crosswinds, tailwind, lowering cloudbase etc etc etc.
Learn and practice all sorts of holds with different entries and winds.
Of course you NEED an instructor!
Trust me when we say that a good instructor is worth their time in gold even with a basic sim.