We got lucky with this basement in that a lot of the structure work was done, and actually done properly. After we pulled out the nasty carpet, I took a good look at the walls. They had been painted beige, and one wall had dark stripes. The stripes were the unpainted rough wood paneling. Ugh! As I appreciated that the previous owner had taken the time to paint the walls a lighter color, I shuddered at the thought of all dark brown walls in a basement with only a few tiny windows. But it was still panelling. You can put lipstick on a pig but it's still a pig. Since there was mold on the carpet, I did myself no favors by researching "moldy basement" on the internet. I ended up getting so wound up about toxic mold behind the walls etc, we pulled off some of the panelling to look behind it. Thankfully, it was all good behind the panels but with one wall in the "office" pulled out, I made the gallant remark "we may as well rip the rest of the walls out, honey". Given the chance for destruction, Wino obliged and out came the walls. We did end up finding some mold on a few panels so the choice was a good one. The walls had been properly studded out and insulated so that was fortunate. I chose to use the "greenboard" drywall. It's supposed to be mildew and mold resistant and is only a dollar or two more. I treated inside the walls with a mold preventative, same one used on the floor. I replaced the bottom foot of insulation due to past water and critter damage. Wino found dried red beans in one wall. That was weird. The drywall was installed after the flooring was finished, mostly so we'd have something to walk on. I did leave the panelling inside the window wells and smoothed it over with joint compound. Removing it seemed like a can of worms best left alone. A few sections of the inside walls were also left up and smoothed with JC, there was too much going on with switches and doorways. It took 26 panels of drywall, purchased at 84 Lumber for a few pennies more than Lowes or HD. 84 is so much closer to the house and it was brought home in bundles of 5 or 6 tied to the top of my Matrix. Good times.
After taping the seams with mold resistant seam tape (yup, they make that, but I wouldn't bother with it again) and finishing them off, we added new baseboard in the main room and recycled the old baseboard as much as we could in the "office". It was stained dark green so a little work went into making that paintable. I added a quickie crown moulding, basically using a smaller base moulding turned upside down. Much easier to install than proper crown and gives the room a finished look.
Where did I go wrong? Well, I would have replaced the insulation with R-19 if it had been really cold out when we started this, but I really didn't think too much about it and there's R-11 in the walls now. I would have been more diligent about keeping the new floor protected because it now has a haze from the drywall sanding and requires some elbow grease to clean. Other than that, it was pretty straight forward. Oh, the studs were not evenly spaced so a full 4' drywall board didn't always line up on studs so there was much measuring and moving seams etc to reduce cutting. I don't think I've ever worked on a house with evenly spaced studs. Maybe they eyeballed a lot more in the past. Maybe.