I never encountered the renown bug myself but I stick to the basic 1 day-shakedown for my first patrol, get a full crew to my satisfaction, load the first patrol, sail around a bit and check whose voice i want for my sonar guy, whether i have 2 officers looking exactly the same (in which case i want to change their faces) etc etc. dock in base, get promoted to Oberleutnant due to the 1500 renown I still have, use SH3 to fiddle with the staff (faces etc), get the improved hydrophone on the VII and then the hunt begins
I save my patrols every once in a while when I am not in contact with anything, on the surface, out in the open seas. that seems to keep things nice and stable, I rarely get CTDs with GWX2.1, except when I overstretch my system by having some other programs running (word, msn, browser with subsim etc) and do a bit of taskswitching.
savegame has 1 purpose: keep frustration down to a minimum should you get a CTD halfway through a patrol which was otherwise going well
hope this helps