I honestly don't think you will need 3 brackets per metre, plus end brackets, plus verticals.
I've just cleared out my wardrobe. The poles are 1m long, and my dress wardrobe had over 100 dresses in it (I have some very thin hangers and far too many clothes), and those poles are only end mounted.
Over a longer length the risk of the pole bending on the middle obviously increases but once you put the verticals in then it effectively becomes like two or three poles.
If you went for the version with 3 brackets for your long pole and two uprights then you'd have:
an end wall mount (mounted in to the side of the alcove)
a wall bracket roughly 40cm in
a vertical approx 80cm in
a wall bracket at 120cm
a vertical at 160
a wall bracket at 200
an end bracket at 240
(I've rounded down a tad)
You've got support coming from 3 angles, and a support every 40cm. That does feel pretty adequate.
You could leave one of those 80cm sections (say between the wall and the first vertical) as a full length section and then buy the individual poles, brackets, end brackets etc to allow you to split the other two 80cm sections in to a variety of different heights - these would let you attach horizontals to the verticals, so the ones in the middle would be supported by two verticals, and the ones in the other end section by one vertical plus one side wall fitting. You could add a single back wall bracket in the middle of each cross piece if you wanted to, but it might not be necessary for shorter, lighter clothes.
Actually, if you wanted more flexibility it might be worth sticking an extra vertical at the very end so that those reduced height sections are flexible without having to re-drill the wall?