There's always one, ME!
I do not care for the "ride" I experienced w/Progressive springs. To harsh for me!
I always cite what my local trike installer told me. Out of 6 people that insisted on Progressive springs, against his advice, when trikeing, 5 have returned and asked for OEM springs to be put back in!
I also found, when I had my 2000SE that I got the best "ride" w/0 air in the forks.
Anyway, to answer one of your questions, use the recommended fork oil and the amount recommended.
For Sgt, from a thread on Steve Sanders forum:
Oil fill with forks collapsed and springs out (from the shop manuals):
239mm / 9.4" for 88-94
194mm / 7.6" for 95-up
Of course that kinda sucks if you've got springs in your bike and you're refilling through the air valve...
... so measuring from the TOP OF THE FORK NUT (schrader valve removed) looks more like this --
Oil fill with forks fully extended and springs installed (measured from the top-plane of the fork nut with the air valve removed):
400mm / 15.75" for 88-94 (Progressive springs installed tight end down)
406mm / ~16" for 88-94 (Progressive springs installed loose end down)
408mm / ~16.1" for 88-94 (OEM springs installed)
* 355mm / ~14" for '95+ (Progressive springs installed tight end down)
* 361mm / ~14.2" for '95+ (Progressive springs installed loose end down)
* 363mm / ~14.3" for '95+ (OEM springs installed)
I Googled how to measure fork oil in 1500 gold wing and that was one of many that came up!