Definitely heed Daggaboy's and Hufnagel's words. Even though you're thinking of a small project Murphy will find a way.
Every time we've gotten something done on our 1980's vintage home we hear something along the lines of "Huh, that's strange, wonder why they did it like that..." Every time. Windows, roof, gutters, water heater, kitchen, bath, decks, even landscaping. We laugh now when we hear it (to the relief of whomever just made the discovery.)
Know your local laws when it comes to permits and code. We found that people in the business, who you would think should know, don't know, or will feign ignorance. If a permit is opened, make sure it gets closed. Otherwise it will cause problems down the road.
When we did our big remodel we were told it could take 3-4 months to get the building permit. It ended up taking 8. We had ordered appliances & fixtures to be ready in 3. So it all sat in our garage while we waited. We were warned we might need a new electric panel. Of course we did, and new wiring. More permits, inspections, and delays. There were issues with the cabinets that weren't found until they were installed, adding a few more weeks. The real doozy was the sewer lines. But you get the idea. One thing leads to another.
For shower fixtures I really like the ones where setting the water temperature is separate from turning the water on and off.