Should the ability to craft slayer rings be my first use of Slayer reward points?
No. Early game Slayer is pretty boring as the monsters down there are mediocre. You can unlock the ability to craft slayer rings and stock up in advance, but you won't even be able to fight the Slayer monsters at those locations.  Even if you want slayer rings for their secondary teleport benefits (Quick access to tree patches and fairy rings), your first use of Slayer reward points should be for primary priorities. Most consider unlocking slayer helmets and superior slayer monsters as better first purchases.