been doing iGaming seo (slots, games, casino brands) for quite a while now, and what i can tell is that there's no right answer about what works the best now. It all depends on the keywords you're gonna work with, because even within the same GEO but with different keywords it can be completely different.
but in general I'd suggest you:
- learn thourougly your top competitors, all the anwers are always there
- in most cases go for fresh EMD domains but also buy some expired ones, although as of today it is as much of a gambling as literally playing in a casino - you may hit the jackpot with a $10 expired .com as well as get nothing with an auction bought domain for a few grand. As a solo, I don't have that kind of money to play these games so I mostly buy expired domains for a PBN, not for money sites. The PBN/Money site domains rate is probably 90/10, I just feel like it is a steadier, safer way to do things nowadays (again, if you're a solo. If you have hundreds of thousand dollars to spend and you're good with choosing an expired domain - you may try to go this way). But anyway, the times when you could buy an expired domain and it would bring you at least some traffic are long gone.
- parasite SEO does work. Mostly it's Trustpilot nowadays, but there are less obvious platforms as well.
- pick your keywords wisely. Obviously, you shouldn't try to rank for some "best online casinos" or "non-gamstop casinos" type of thing.
- the number of websites matters. The more websites you've built - the more experience and understanding of what works and what doesn't you have. Although, don't just mindlessly generate hundreds of shitty websites but try to understand what works better within your GEO and keywords and expand on the successful tries.
- always be testing something and write notes on what you've tried, what the idea was behind this (if any), and how it worked out. I've seen lots of things that seemed like they make absolutely no sense and would never work but they broke Google somehow and brought those FTDs.
So, overall it's analyze, go for a reasonable, realistic competetion and try, try, try.