Not quite sure what you mean by your first question.
Active Runway is in FS only determined by the wind and weather, so if you have real world weather activated you'll get different runways as the weather changes.

If you're flying IFR, the ATC will asssign you an approach (you can choose another one if you'd like) so you have plenty of time to adjust, don't forget ATC will also  vector you to the runway.

The last question is a NO, at least I haven't noticed any runway assignments based on my airplane. C175, b737, ATC would hand me the same runway regardless.

If you're flying IFR under direction of ATC they will select the runway based on wind and weather as was said above.  Your approach to the runway depends, at least in part, on your direction of travel.

For example, if you're approaching the airport from a direction opposite the assigned runway ATC will take you through a hook shaped approach.  ATC will have you fly around the airport and eventually turn you to a course that is 90 degrees off the runway.  A few miles from the localizer they will tell you to turn to a course about 30 degrees off the runway heading.  From there you intercept the localizer and continue with the landing.

If you're flying straight in ATC takes you through a similar maneuver to put you on a heading 90 degrees off the runway so you can turn to an intercept course.

gw

"The last question is a NO, at least I haven't noticed any runway assignments based on my airplane. C175, b737, ATC would hand me the same runway regardless."

I dissagree, at some airports atc will assign you a runway based on the the size of your aircraft KCCR being at least airport that does this, a 152/homebuilt up to a Baron will get the smaller runway while anything over aBaron will get the longer runway