Everyone has preferences when it comes to their tools of choice. Here are the items I think are essential for window sash repair.
Starting in the back.
Epoxy filler. Hopefully your windows are in good shape and you are decay free. But then you wouldn't be in need of restoring your sash if it were in good condition...would you? Let's just say...."I hope your decay is minimal." Out of the six sashes I am currently restoring, 3 were decay/rot free, 2 had minimal damage, 1 was in bad shape. I am still working on that one, filling the bottom rail edge. When I reinstall these sashes I will look and see if I can discern what is the cause. The sill is rather flat and water might be trapped between the sash and sill. All my double hung windows have sills with a 7 to 8 degree slope. How do I know that??? I used a digital protractor to read the degree of slope (incline/decline). When I called to order wood storm windows I needed to know that. But I believe the biggest contributor to the decay problem is the fact that neither the top or bottom of the sash have ever been painted. Exposed end grain is a recipe for decay. I can't correct the sill slope but I can seal the top and bottom of the sashes.
Dremel with a barrel/drum sandpaper bit. I used the Dremel to remove stubborn glazing compound. Just remember to keep the bit moving and use the low speed. I also used the Dremel to smooth any wood that looked a bit jagged after glazing removal.
Palm sander. Actually I wish I had purchased 2 of these when I bought the first one for $10.00. If I had two, I wouldn't need to change paper to change grit. I like the palm sander but it is a knuckle scraper and fingernail breaker when it comes to changing the paper.
C clamps and bar clamps. These make or break a glue job, especially if you are using a glue that expands as it cures. Just remember to use paint sticks to protect your wood from the clamp load.
Razor blades and razor blade holders. I have several razor blade holders that I alternate between. Some holders are more comfortable than others to work with. Unfortunately for me, the one that works the best is the one that is hard for me to hold. I also buy my razor blades in bulk. The box of blades in the photo cost $6.99. I bought that box years ago. I don't know right off hand what the cost is for blades in 5 or 10 piece increments. But I have to believe that after buying several packs you have invested what a large box will cost. I use razor blades for scraping the paint off the glass before I reinstall the panes. Razor blades are also one of the many tools I use for glazing removal....sometimes glazing removal requires throwing the entire toolbox at it. I also use a razor blade to lift the glazing point up off the glass so my needle nose pliers can grab it.
Putty knives. Plastic or metal....I use both. The metal ones come in flexible or stiff. I use both. Invest in a quality stiff metal putty knife, you can use it later as a scoring tool when marking for mortising hinges etc. I use Hyde brand at home and on my job. They are sturdy enough to withstand light blows from a hammer. I also grind a sharp edge on a stiff putty knife using a grinding wheel. This comes in handy for removing the tongue from tongue and groove flooring. This will save your expensive chisels.
Glazing tool. This tool can be used for glazing, installing glazing points, and opening your can of glazing compound.
Cheap paint brushes. You'll need one to coat the wood with your sealer of choice. I use boiled linseed oil, but paint primer is another option you can use. Also I like to use a disposable paint brush when I am painting with an oil base primer. Rather than spend time cleaning the brush with mineral spirits, I just toss it. Cost less than a $1.00 and I didn't have to make a mess trying to clean it. I also use the disposable paint brush to sweep out any remaining debris before I reinsert my panes. You could also use a shop vac for this, but my cats don't like the noise and if you have pets....well...you know they rule. I also don't like the possiblitiy of putting additional lead filled dust into the air. This is especially bad if you use your shop vac elsewhere at a later date without cleaning the lead based paint dust from your shop vac. "Like I have time to CLEAN my shop vac."
Glue. I used Gorilla Glue for gluing loose joints. All six of the sashes needed gluing of some type. Most needed the top and bottom rails glued. I used the bar clamp when I glued the rails. Also some of the muntin bars were cracked and needed gluing. For the muntin bars I used the C clamps and just enough pressure to close the crack. I let any glue that has oozed out dry and later removed it using the Dremel.
Small needle nose pliers. I have a pair that I bought out of the discount bin at the local hardware store. They are the perfect size for removing old glazing points. My regular needle nose pliers were too thick to get between the glass and the glazing point.
Time invested in the last several days....1 hour 30 minutes. Total time invested.....33 hours 30 minutes.