The grub screw on my first brick was the first thing I had to confront even before bringing it home.
If it is any consolation to you, the job took less than 8 hours start to finish working in my son's driveway. As I recall, it is all pretty straightforward and the hardest part of the job was getting the grub screw back in. I think I dropped it off the end of the Allen wrench about 10 times before I finally got it started in the shaft. Most of the time was spent carefully removing parts and putting things back together properly. Total time messing with the transmission was less than two hours. I could probably knock two hours off the total today, since I had never been in a brick before tackling the job.
My only advice is to have a box of zip loc sandwich bags and a sharpie pen to label the hardware as you disassemble things. It will make reassembly go a lot faster to have what you need all together. Since you will be dropping the screw into the transmission a couple times, you will need a means of getting it out of some tight places. A small retrieval magnet or very long tweezers.
Besides your tools, you want to have transmission oil, anti-seize, spline lube if you haven't done them recently, Blue Loctite, Brake Cleaner to degrease the grub screw and the shaft it goes into, some Permatex black gasket maker, and a couple rolls of paper towels for wiping things down. It would also be nice to have some sort of stand where you can have the transmission standing on end when you split the cases.
I suspect the screw has been getting loose since you got the bike, so you will be in for a pleasant surprise when you get it tightened up. The shifting will be so much more positive.
Keep your spirits up, you are bringing a neglected brick back from the abyss and soon she'll be repaying you with miles and miles of roads pleasantly put behind you.