I travel for 4-1/2 months at a time but not before early April (and that was Andalucía) or after September, so I don't have to worry about really cold weather. My pills weigh at least 6 lb. when I head out, and I never have time to fully consolidate my travel information, so there's always considerable paper weight accompanying me. This forces me to keep clothes to a minimum. The only shoes I take are the ones on my feet (good quality athletic shoes, as close to solid black as I can get).
I use a set of long johns under summer-weight clothes when I need extra warmth. My warm layer is a black fleece jacket. If I'm really worried about cold I throw a packable down jacket in the bag; it scrunches up really small. I wouldn't take two warm garments that couldn't be layered (so not 2 sweaters just because they're different colors).
I was really pleased at how well my new PrAna 97% nylon slacks worked in both hot weather and (with long johns) cold weather. They did a decent job of shedding water (I stayed dry on a couple of very wet long john days), they're light to pack and they dry quickly after washing. I plan to take two pairs on my next trip. There are other brands using similar fabric. Columbia uses 96% nylon, and their pants are lighter in weight but seem to wrinkle more. I suspect they wouldn't be as warm in chilly, breezy weather.
I am not a fashion plate at home, so I know it's different for others, but: I do get bored with the limited selection of clothes I have with me (3 bottoms and 5 tops, more or less), but I don't give even one thought to what I'm wearing after I've gotten dressed and left the hotel (unless I'm cold). It's only when I contemplate what I'm going to put on that I think, "black and white again". I don't do scarves, but they are an excellent idea.
I take at least one compression cube and use if for things that I don't mind wrinkling. That doesn't help with weight, obviously.
It's fine to wear heavy clothes on the plane if you're worried about exceeding the airline's weight limit, but don't forget that those clothes will be in your suitcase if you change locations on a hot day. They need to fit.
You can save a lot of weight by not over-packing toiletries. Calculate how much you use per week or month and only take as much as you'll need. Use hotel soap and shampoo if you're not picky. If you're not willing to do that, consider packing enough for a month and trying luxurious local products when you run out. Use solid products rather than liquids whenever possible. I've seen US brands of toothpaste all over Europe. I have not found travel-size solid anti-perspirant, so I now take three with me.
You should start a list of non-packing-related things you need to do before departure. There's a lot: insurance payments, property tax payments, arranging for someone to pick up your mail, auto-payments for any monthly or quarterly bills coming in, auto-payments for your credit cards, travel notifications to your bank and credit card companies, extra prescription drugs in case you somehow don't leave Europe on schedule, scheduling medical check-ups that will be due right after your return, etc. You don't want to suddenly remember something important on the day before departure. Also, check to be sure the outer jacket you plan to wear to the airport is actually hanging in your closet before you're ready to head out the door. Mine wasn't. I still don't know where I left it.
If you haven't already done so, check with your bank and all credit-card issuers about international-usage fees so you know what will be the least expensive way for you to pay for things in Europe.