I've always put "plenty." Too little and it might not have the desired effect, too much and... it just squeezes out?
Sounds like you're talking about the bit at the top of the "two-position" post, where the seat post head is attached to the post.
The saddle height should be adjusted at the frame clamp where the post enters the frame, not at the top.
Sounds like you're right, you need a new wedge at the top. If you're the ...
Yes, it's okay. It's because the wedge works by expanding front to back, but since the two wedge pieces are on an angle, it also expands top to bottom. So it gets taller as well as wider.
Good idea on the carbon paste, it's practically a necessity in modern bikes with carbon frames and carbon posts.
Last idea - check that ...
Possibly left lever operating the rear brake in the UK. So the cable housing bends a little tighter from the left side of the handlebar to double back and enter the left side of the top tube.
I think I see a crack there? Should be included in the warranty I would think.
Are you the original owner? How many miles or kilometers?
I wonder if your rear derailleur hanger might be a touch out of alignment? I've had a pulley constantly catching an off-angle chain making a whirring sound that stopped after aligning.
Stiff sounds like friction, of which there's more with left-rear, as you mentioned. I like to lube the cable with very light oil, but sounds like you've tried that.
Crunchy sounds like possibly a coil in your housing has gotten out of place, which can happen routed either way. If it's at the end, trim it back a bit. If ...
Many new chainrings have that whirring sound (great way to describe it actually!) until the edges of the teeth become naturally buffed by the chain's normal action sliding over them while pedaling. Keep riding, it'll get better.
My new SRAM 50-34 was downright crunchy for the first 200 km or so (guessing on the distance).
I've often ...
Small scratches are normal, it's not necessary to protect against them.
EM3 is right, to get a complete diagnosis.
But sometimes it's worth trying the easy stuff, even without a diagnosis. You know, because it's easy.
Try pulling the crank and putting some grease on the crank spindle where it runs in the bearings.