I think the 1911 is a must have.
As far as "must have" options - I think that like Hillbilly has indicated, everyone is going to have a completely different list.
One thing I look at on a 1911 is the slide to frame fit. I hold the weapon in one hand, wrap my hand over the top of the slide, and check the left to right ( lateral ) fit. If it rattles or is "loose" feeling, that is a problem for me. I like a tighter tolerance on my pistols, but this is personal.
Some people will tell you that a loose tolerance will allow the weapon to run if it's dirty or has been dropped in the mud.
While I can see their point, having a loose tolerance also allows for dirt and debris to get in there in the first place.
Another thing I look for is how sharp are the edges on the weapon? Are there any significant edges that could snag or catch on clothing, or worse, my flesh.
I got a buddy who bought a carry 1911, Commander style, that was built up by a local gunsmith for a friend. My buddy happened along at the right time and got this gun for a steal, NGIB stylez. The gun runs like a swiss watch, and it shoots like a dream. Rounds on target all day long. But that damn thing is like trying to handle a rabid porcupine on crack! I can't hardly look at that damn thing without getting a new scratch or cut.
Obviously this would be a feature you would want to avoid.
Like most of the people who have come from the cave and into the light of the genius of JMB, I think you will just "know" it when you feel it.
You probably should shoot a couple before you decide. Try a couple of different models, a couple of different sizes and configurations. Once you find one you like, then shop around for what options are available on that model and see if they would be beneficial to you.
Good luck and keep us posted!!