A backup you have never restored is only a hopeful file.

What to check next

We started by reading the code rather than the documentation, because the code is what runs. Most of the surprises in a WordPress project live in the gap between what a function promises and what the theme actually asks of it. An hour with the templates open told us more than a week of status meetings ever had, and it gave us a list of real questions to bring to the client.

The first measurement is always the most useful one, even when it is rough. Write down the query count, the page weight and the time to first byte before you change anything. Without those numbers you cannot tell an improvement from a coincidence, and three weeks later nobody will remember what the site felt like before you touched it.