How to actually do these today
Pick the top three from the list. Block off two hours. Do them in one sitting.
The trap is reading the whole list, getting excited, and then doing none of them because you decided to "audit the whole site" instead. Audits are how websites stay broken for another year.
Three fixes is a real afternoon. Ten fixes is two afternoons spread across the next two weeks. That is genuinely all this takes.
If you want help
We do this all day. We can audit your site in an hour and tell you which three of these to do first for your specific business. Sometimes that is the entire project. Sometimes it is the start of a bigger redesign.
Either way, the most expensive website is the one that has been collecting dust for three years while you keep meaning to fix it.