Kathmandu has a ton of trekking stores where you can bargain your heart out for fake north face gear. If you make it up past the first 2 days of hiking to Namche Bazaar (if you're doing everest base camp), you can pick up stuff for even cheaper there.
I WOULD say get a good pair of hiking boots NOW if possible and break them in as much as you can before you have to wear them and walk in them for 6 hours a day for 10 days straight.
I did 14 days up to Everest Base Camp and down the next valley (Gokyo...AMAZING) and had hiking shoes, some good socks, crappy pants (thin and chilly!!), a fleece + shell combo, gloves, and a warm hat. I stayed in teahouses along the way...some of them have blankets but it might be nice to have an extra sleeping bag along with you.
Which trek are you doing? The route I did was fairly straightforward - the one really challenging day was the mountain pass over to the next valley, and the biggest problem you'll have is probably acclimatizing to the altitude, which can definitely be an ass-kicker.
Let me know if you have more questions! Hiking the Himalayas was one of the most amazing and challenging things I'd ever done, and I'm sure your experience will be great as well.