I had the same iMac model with the intention of dual-booting it to run Windows for gaming (and certain other software that had no Mac equivalents or only poor equivalents, but mainly gaming). It worked just fine for older games when I had Windows Bootcamp that I also ran in macOS using VMware's Fusion. You're going to need more RAM. Happily, you didn't pay Apple for it (neither had I) and it's trivial to find, buy, and install the necessary RAM. I'd recommend adding 32GB (2x16GB sticks) on general principle. As you mention, you're not hurting for money.
Anyhow: mine worked fine for older games, but running them in Bootcamp is infinitely better than running them in Fusion. Regardless, I did end up selling it, buying an M1 Mac mini and a dedicated Windows PC for those tasks. Mainly because I'm waiting on Apple to deliver a 32" 6K iMac... however long that ends up taking. (Turns out I really jones for giant screens)