Good question. Generally, the gear should be down before starting down the glideslope at the FAF (Final Approach Fix) for an ILS (or any approach), whether it is coupled (flown by the autopilot) or not.
The easiest way I have found is to use a heading bug that will intersect with the approach.
Then on the g3000 You need to have the VOR1 selected as the nav type (CDI Source). If your in nav mode then you see a pink/purlpe line (Arrow) in the display compass. If your in VOR mode you will see the Grean line (Arrow)
Once the green line starts to line up with the rest of the arrow I press the APPR approach button on the Auto Pilot.
I’ll add a couple of pics But im not in range of my destination airport so Please forgive the Pics. Im also in a Kingair with the G5000 of the top of my head.
But the principle is the same.
No. Not even heavy airliners have the gear down when intercepting the glideslope.
Way too much drag and too slow.
IRL the aim is to be established in landing configuration with the correct speed in bad weather (you can’t see the runway) at 1000ft and in good weather at 500ft.