1. Keyboard entry is where you create the object, parameters is where you edit the recently created object. It would appear that if you change some of the parameters on an object, some of them are remembered for the next object you create, though not all.
Personally, I just select my primitive type and drag-create it in the viewport. Keyboard entry is rather restrictive, in an artistic sense.
2. Not entirely sure what you mean there. If I apply a modifier, then I adjust the settings using the modify panel on the right. If I use one of the poly tools available in the modify panel ( such as 'bridge' or 'connect'), then I'll use the little pop up window. That's fairly new, though.