I was kind of wordy. My basic point is "match the set of parts by quality and life expectancy". If you install new seats to last 20,000 miles (2 years) but the guides are only good for 5,000, you're not getting what you thought you were going to get. The way to do it, I'd say, is to inspect everything, make a list of what's needed and what gets you where, and execute a plan.
And if you have an undesirable head, you might not want to spend any money on it.
I'm just the voice of economy. I ran my coolant leaking N42 head for 20,000 miles on two cans of Barr's StopLeak, instead of pulling the head to replace the head gasket (when I would have also found that the head was warped). Then replaced the whole engine when I got tired of it and was sure that my spare engine was in much better shape. I was in your boat at the time. Low cash flow.