I think you should start with the basics. Learn how to evaluate backlinks for example. Don't expect to pull of advanced techniques if you don't know what you are doing.
If you want to rank only a landing page, then expired domain won't be too much help. Ranking 1 pagers or very small websites with barely any content is rather hard these days.
How strong a domain? As strong as you can afford. The more competetive niche, the harder you have to go. Still, unless you have at least $500 - 1000 to spend, then do not expect the domain to do much, if anything at all.
Strength of the domain, for the sake of simplicity, can be determined by number of referring domains and let's say domain rating metric from Ahrefs. Forget DA/PA and other MOZ bollocks.
The higher the RD, the better, the higher the DR, the better. Still, you should really learn how to evaluate backlinks as these numbers are good only as a basic filter.
Here is some basic checklist about what to look for - https://www.blackhatworld.com/seo/what-is-your-checklist-for-domains-for-pbn.1342695/#post-14514468
And this is a decent guide on how to use those domains - https://www.blackhatworld.com/seo/guide-how-to-use-expired-domains-effectively.1223248/