Get a copy of Working Windows by Terry Meany
https://www.amazon.com/Working-Windows-Guide-Repair-Restoration/dp/1599213117
No the pulley does not reduce the effort. The weights (and the sashes) essentially hang free within the jambs and weight pockets. So you want a balanced system (the mechanisms in modern lift sash windows are called "balances"). If an individual sash (upper or lower- doesn't matter) weighs a total of ten pounds then you use a pair of five pound weights for that sash.
When I bought the house, the four front windows on the front of my house were entirely painted shut. I decided I wanted to pry them open and make them work (and I figured if I was going to the work of doing the bottom sashes, I should do the top sashes too). I bought this book from Amazon, and between the book, This Old House tutorials, and various other online resources I figured it out!
I spent a lot of time stripping those four windows (eight sashes!) with a heat gun, reglazed the glass and everything. The other three windows I did and the kitchen window were in better shape, so I stripped the paint with scraping and a belt sander and didn't have to reglaze the panes... though I probably should have reglazed the kitchen upper, but I got lazy. I've replaced a few other ropes here and there -- thankfully in an old house, the weights are usually in the weight pocket even if the rope is broken.
My biggest advice is that the parting bead (to hold the uppers in place) breaks 90% of the time trying to pry it out, and sourcing some new stuff will make your life way easier than trying to be super careful with the old stuff. Same with the window stops for the bottom sash -- between caulk, paint, and inevitable secret nails, it's way easier to just pry/break with abandon and replace with new.
Please don't replace those gorgeous old windows! Even painted shut, that old-growth, tight-grain wood will never be had again. (And if they're half-rotted, you can use special epoxies to completely restore them.) Are your sashes weather-stripped with zinc or bronze? If not, that's a must - it will make original windows nice and tight.
Believe it or not, properly repairing your current old sashes & adding/repairing good storms is just as energy efficient as replacement. Plus, it's loads cheaper and they look better (more in context with the historical appearance of the house). There are two fantastic books that walk you through a DIY, if there's no local glaziers:
Also, this book by George Nash is invaluable. I've referenced it while we restored several 70+ year old homes, and have bought copies for fellow century-home friends.
I just finished a complete in-place restoration of our current WW2 bungalow's windows -- stripping 250+ lights all the way down to wood, and then reglazing/repainting. Sounds like a huge job, and it was because we did it all at once, but if you tackle one window at a time on the weekends, you can have the whole home done in short order. With semi-regular maintenance (spot glazing touch ups in 20 years) this job will last for another 70 years. One of the reasons we bought this house was because the windows were original. There's nothing worse for an old-home buyer than seeing a house that's had all of it's character & craftsmanship stripped away. Character includes original whenever possible - windows, plaster, molding, etc.
If you do decide to replace, please consider taking the sashes to an architectural salvage shop (or antique shop) so they can be used again.
Feel free to PM me if you have any questions. We've seen it all.