My opinions:
1&2 having the belt loops spread further apart is preferable. It keeps the gun more stable and in the same location. I found a loop or loops on the holster body less comfortable, plus it seemed to make the holster thicker.
3 comfort? That should be a top priority for IWB carry. There is no way I want Kydex next to body.
4 your belt tension should provide sufficient tension to keep your gun where it's supposed to be
I have tried multiple designs over the years and settled on this:
https://www.ttgunleather.com/product-page/reinforced-iwb-mikes-special
The "sweat shield" up top between the slide and your skin is essential, especially if your pistol has a thumb safety. That tab at the bottom/back helps keep the grip in tight to your body. Snap straps are easier to put on/take off. The steel reinforced mouth for re-holstering is not essential & I think I have only one of those. I do have another Mike's Special as well as IWB holsters from another maker that have all of the other features.
I have tried the plastic clips on a "tuckable" IWB holster but they did not work well for me. Metal clips
All that said, the Milt Sparks Summer Special style is very popular for IWB carry. Mike's Special just works better for me.