unless you’re building a pimpy SS just for the hell of it then you’re over thinking it….
It’s for a single speed, if you haven’t got a chainset in the shed you can use, and none of your mates have either, then just find a cheap and cheerful 2nd hand Shimano Deore/LX or similar on eBay for ~£15 and put a decent SS unramped ring on it. Look for 104 BCD 4 bolt cranks as already said as choice of chainrings is wider.
Total cost should come in less than £40 for cranks, ring and chain easily, and will work fine.
If you’re not building a budget SS for winter grinding-paste longevity and want something posher for the sake of it* then just set your budget and buy whatever takes you fancy at that price and fit an decent SS ring.
*equally valid reason in my eyes 🙂