In reply to ConnorMak:
All just my opinion and what works for me (sometimes)...a lot of winter is spent being too hot or too cold, the goal is to stay dry not warm.
I'll assume you've got well fitting, comfy boots already. If not then that should be your priority imo. Good boots combined with pack-a-mac w/proofs and charity shop joggers/fleeces beats borrowed badly fitting boots with gucci clothing every time.
Second thing to spend your money on (imo) would be a thick belay jacket.
There's no perfect combination of clothing for scottish winter and you'll end up with a set of different clothing for different conditions - you'll just be uncomfortable sometimes until you get there! You mentioned rab vapour rise trousers which are a good example. Perfect in a lot of conditions but if it's a wet damp day or you go practicing ice axe arrest in damp snow then they'll get wet and you'll get cold. They would be a great winter trouser for you but get some long johns to layer underneath if it's cold and buy some w/proof over trousers for if it's wet as well (generally to go over the lj's). You've then got 3(or 4) combinations of what to wear - rab vr alone (dryish weather), rab vr with lj's underneath (dry and cold), lj's and w/proof trousers (wet!). You could wear the vr with the wproof trousers but that wouldn't work for me, too bulky and it's a warm combination (if it's wet enough to need wproofs it wont be that cold). If you can't budget for both then go with w/proof over trousers and jogger bottoms, fleece trs or long johns. You can pretty much go out in any scottish winter conditions in joggers and over trousers, that can't be said of softshells. 90% of the time I wear lined non-zip up wproof trs with merino long johns and quite a healthy build up of duct tape around the ankles but then I'm a cheap skate and I hate faffing with trousers or getting changed throughout the day. Usually too warm on the walk in and too cold on the route so must be about right!
You can be pretty comfortable on your top layer for very little money. i would forget the soft-shell unless it's something you really want and get a decent fitting hard shell. A close fitting micro fleece with a base layer underneath and a hard shell on top would be comfortable for most people when moving. Your clothes need to fit really well, it makes a huge difference and a baggy wproof jacket really wont work as well as it should. A lot of people make the mistake of putting thick layers on when you're moving around, on a walk in I'll often just wear a base layer. If it's not raining and you've just got a base layer on you'll be as dry as you can be. You get cold as soon as you stop moving but you just put on your belay jacket. If you get really cold while moving you can just cut the wind out with your wproof jacket. If you're very fit and you expect to be with people that aren't then another insulation layer under your hard shell is an option to keep you warm if you're moving slow.
Hands. Do a search on here for gloves in the winter forum and make a big pot of tea, there's a ton of cheap options and I personally avoid anything waterproof and climbing specific. You just end up fighting with wet twisted liners. Many cheap gloves are a better option and something like the £15 yellow leather sheepskin lined style "guide" gloves are great. A cheap pair of mitts work very well, it's nice knowing that even if all your gloves (and your mitts!) get soaked then you can stick your hands in your mitts and they'll still keep you warm enough. A wet pair of £80 wproof climbing gloves with twisted liners is the ultimate kick in the balls when you're out and about with people wearing £5 freezer gloves and £10 mittens from aldi with warm hands! Oversized washing up gloves with liners in work well in the wet too. If in doubt just take lots of fleece glvoes and dump then in the bottom of your bag when they get wet.
Bolle do some clear lensed safety goggles you can pick up for around £10 which is all i've used, they're shit and they steam up but occasionally you can see better through steamed up goggles than with bare eyes. It's rare (for me anyway) to find the kind of conditions where you really need goggles apart from the half an hour after a top out while you're getting to lower ground. I've looked at nicer goggles before but I'm not quite ready to believe that spending 4 times as much will mean you don't get condensation-maybe i'm wrong a lot of people swear by clear goggles. I've slowly crawled out of a cairngorm plateau hoolie with a merino buff pulled up over my head under my helmet like a sock/tunnel in front of my face before because I was getting so pissed off with steamy goggles that I ditched them. It worked surprisingly well. Some people swear by their goggles though so I'm probably just not doing it right, I believe keeping them tucked close to your skin so they stay warm can help.
Dry bags and packing. I used to have a drawing of the inside of my bag that I packed away on top of my winter kit at the end of every winter so I could remember what order to put everything in when the next season comes around. You dont want to be digging around in the bottom of your bag for your water or depositing the contents of your sack in the snow while you take your fleece off. When you're walking in you'll have your walk in gloves on and a hat,you'll need access to your water (dont put it next to your crampons ;p), access to your wproof jacket if its not on, map/guidebook and your belay jacket if you stop. So they go at the top. You'll pur your crampons on at some point, you want your wproof trousers above those if you have overtrousers to put on. If you're putting your crampons on you'll probably have your axe out soon, so you'll want some thicker gloves to stop the metal cooling your hands. You're probably going to start moving slower as well so it'll be time for your mid layer etc. etc. Belay jacket always at the top, its a lot of weight to carry if you're not putting it on every single time you stop, if you cant drop your sack and put it on in 10 seconds you're not getting the most out of probably the best piece of winter kit every invented.
Most things dont need to be kept dry imo so you only really need a dry bag for your mid layers and gloves/hats etc and a small one for your phone, car keys, spare batteries and torches. 20ltrs is a good size, you can roll a 20ltr bag down to 10ltrs but you cant expand a 10lrt bag to 20. I usually use freezer bags for my food, in my belay jacket pockets usually - saves you being the guy whose tuppaware box lid is flying through the air while they're trying to cram the rest of their snow covered kit back in their bag before it blows away. Quickly sliding your belay jacket out of the top of your bag and you're all toasty warm eating your lunch in no time.
Quite a lot of climbers manage with 25-35ltr sacks - rack, ropes, helmet, clothes, food etc. Don't carry too much. I would go winter walking with a 20ltr bag - not saying do that (if the MR say take a 45ltr sack then I'm not going to be the one to say otherwise) but just as an example of the kind of kit you want to lug around on your back. If you're stuffing a 45ltr sack full you've got too much and everything will be worse, you're legs will take more strain, you'll work harder, sweat more, get colder... Things dont pack as well in dry bags, ask yourself how bad is it if this gets wet and how likely is it to get wet?, in anything but torrential rain then i don't usually fully do my dry bags up or i squeeze things into my bag and then roll the tops up once they're in. Don't forget a bag for your rubbish, nothing worse than finding a rotton bannana skin tucked into the side pocket of your rucksack two months down the line.