2 questions: fleece vs down and caldera cone

It depends a lot on your metabolism. If you are like me and generate lots of heat as soon as you start moving, then anything heavier than the very lightest fleece is for in camp – and in camp, down is king. But if you are not such a furnace then it may be a different story. Personally I do sometimes take a light fleece – actually an expedition weight long sleeve zip-t, which is about the same as 100 wt fleece – to augment my light puffy on spring ski trips. Rarely do I wear it on the move, but occasionally I do if it's breezy and I'm on flat terrain. Soon as I start up any kind of incline I'm back to base layer unless it's snowing or very windy. I have never been out in weather in which I could wear a puffy jacket while moving – I expect for me that would have to be below zero F.

Where I like the light fleece is for breezy and somewhat chilly – say 30's or 40's – where just base layer is a little too cool. I could wear my shell but that gets sweaty pretty quick, where the light fleece lets so much breeze though (but not all of it) that I don't overheat. Then when I stop for a break, whip the shell on over it and Id don't cool off too fast. And it's easy to start off again with the shell on to warm up, then take it off while moving and tuck it through my shoulder strap without having to stop.

Caldera cones are specifically made for the pot you are using, let them know what pot you have and which cone system you want.
You don’t want to hike in down as you know, it would depend on how cold it was if I were to bring fleece. Here are some free videos by Mike Clelland that you might like to watch, the 3rd one is on clothes video tutorials

Andrew Skurka’s Core Backpacking Clothing || Intro: With just 13 items, go anywhere in 3-season conditions

And Dave Chenault’s BLOG On Skurka’s Core 13 clothing choices

On the subject of fleece vs down.

I always bring both except for hot weather trips.

I very rarely wear down while hiking unless I have to hike slow because of injury.

I will often throw on the down for breaks in cool weather, as well as camp and sleep attire.

My hooded down sweater supplements my quilt/sleeping bag and means I can get by with a lighter hoodless bedding. I can extend my summer sleeping bag down below freezing this way.

What about some of the more breathable synthetics like the Nano Air or Atom Lt, or thermoball where getting it damp isn't such a big issue?

"What about some of the more breathable synthetics like the Nano Air or Atom Lt, or thermoball where getting it damp isn't such a big issue?"

For all puffies, your sweat will cause the loft to collapse a bit (or a lot depending) compromising how effective the garment may be.

A rough rule of thumb = when at rest/in camp/sleeping, wear a puffy. When moving? Fleece.

Personally, I find a 100 wt fleece works for me. Use it when ski touring and in cool and/or misty conditions.

It's a common mistake to try to go for items that "do it all" when trying to go light. Go for systems that do it all instead. A versatile system is made of specialized items that do one thing and do it very well. And can work together to actually, really "do it all".

The problem with active vs non-active insulation is not only moisture accumulation and loft loss in the high loft garments but also moisture management and how this affects perceived comfort. A high loft garment, be it down or synthetic, will be shelled inside and out and this shell manages moisture poorly, feeling clammy. If you need a shell in your active wear system, it must be the outermost layer. The insulation layer must be non-shelled.

Understanding layers needs identifying the different roles that must be covered and the possible synergies between the chosen items.

Once again, think of layers as a team that works together. Carrying both fleece and down/synthetic high loft insulation is not only far from redundant (different roles), it's also how each garment influences each other so for example in case of taking the fleece you can use a thinner down jacket than you probably would otherwise.