There was a story on the american website backpackinglight.com about a couple taking a baby around the pyrenees. There was a discussion on the forum about what equipment they should take, what safety procedures should be followed etc. Some people were dead set against the idea and thought it was tantamount to child cruelty, others were very positive and helpful. I don't have the link I'm afraid, but it might be worth a look for some tips - I think the couple might have been dutch?
I think one useful tip was taking a poncho as a waterproof?
I think you could get sufficient kit for an overnight into the OMM25, but you might have to take different kit. E.g. do you really need a VR top, and a windshirt and a waterproof jacket? Could you ditch the windshirt? Or could a lighter waterproof jacket take the place of two (e.g. Marmot Mica, Rab On Demand Pull on)
Do you need the dynamo, or would a synthetic vest be sufficent? Do you need full-on waterproof trousers, can you make do without, or would montane's windproof ones be ok? Do you need a bulky pair of gloves and a thin pair of gloves?
Of course, clothing choices depend on where you are going and what the weather will be.
My partner packs his waterproof gear into a exped dry bag and compresses it down before packing, and does the same with his 'insulation' gear.
I also obsess about volume, but my clothes are tiny, so it makes it easy! Tents, on the other hand! Oh for the perfect tent...! light, bombproof, small pack size, short poles, heather-proof, space to sit... so far I have not found it to exist!!!
Here's an idea: can you hire boots at your winter course? When you are on the course you will pick up loads of tips from your guides, and they will be really well placed to inform you on your boot choice. If you get to hire boots and find you don't like the fit, that will narrow down your choices.
I might be wrong here, but I was under the impression that the boot you linked to - the Karakorum boot - is a european specific fit, and not sold in the UK?
I was in a similar conundrum to yourself earlier this summer, prior to going on a week long alps course. I got some Nepal extremes, and they are great for on the glaciers and snow in summer alpine, but for doing long walks on rocky ground, they test your feet quite a bit. I thought I might want to do some ice climbing at some point as well. But I have realised that they are too stiff and heavy for more general stuff, and now I am looking for something that I walk and scramble in. It's proving difficult to find something that is stiff enough to cope with the cuillins, but grippy enough to cope with peak district peat
The other thing is fit - I tried on some trangos and they felt so floppy that I never thought they would cope with crampons all day.They also didn't hold my toes in place, so front point would have ended up with blacked and bruised toes.
My partner has the generator vest and he really likes it. He finds that Rab clothing fits him slightly better than montane clothing. Actually, Rab is like made-to-measure clothing on him, and when wearing insulation, that means it works better.
He always takes out his vest, and a montane oryx fleece as his insulation, for wherever we go, be it mountains in the alps, car camping, or doing photography in the peak district. He also has a Rab belay jacket, but that hardly ever gets used.