I would like to put a double cord-drawn curtain track in a bedroom,
with heavy drapes/shear combination, but I am somewhat unclear on the
best method of installation.

(The wall is timber-framed, with gyprock/drywall on the inside, with a
steel casement window, if this makes any difference). The window has
~4 inch wooden trim above and on the sides, and all the current
curtain rods and tracks in the house are attached to the trim at the
top.

This particular window is 285cm (112 inches) wide (from outside of
trim to outside of trim). The drapes will have a triple-pass lining
sewn to the decorative fabric, be ~2.3m long (lining a bit shorter),
with a gathering ratio of ~2.

The available tracks that I can buy at my fabric store are 200-290cm
(with 2 centre supports I believe), or 290-380cm (with 3 centre
supports), and I would need to buy double brackets separately to
convert to a double track. I am going to find out tonight if I can buy
extra centre supports individually, if needed.

Where is likely to be the best place to attach the track so that the
weight of the drapes doesn't pull the track down? The wooden trim or
above the trim, into the wall?

If I attach it to the trim, I would need to use the shorter of the
tracks-would 2 centre supports be sufficient? Could the trim be pulled
away from the wall over time?

If I attach to the wall, I could use the longer track (although not
much longer due to a perpendicular wall nearby). If I need to attach
the brackets to the studs, they may not be evenly distributed, would
that be a concern?

I will be making the drapes, and their exact length is not an issue.
But I have never picked/installed a track before, so would appreciate
any advice.

TIA,
Karina