I echo @Adam_Xett, your goals should drive your purchasing decisions. V-carving requires v-bits, 3D reliefs require ball mills, while prismatic carving just needs square end mills, with other project types requiring other bits.
For me, (I started about a year ago with zero CNC experience) I started with 1/4" and 1/8" square end-mills, and then added bits as projects demanded them. Today, I have a good assortment of square, ball, V, engraving, two different styles of drag knives, and other specialty bits, just from various projects I’ve done. Buy good bits, and they way outlast the initial project they were purchased for, and you end up with a collection that handles 95% of your spontaneous needs.
Don’t forget to factor in software purchases as well. The Nomad comes with MeshCAM and Carbide Create, both of which are awesome for their intended purposes. MeshCAM is great for cutting files from CAD files, and CarbideCreate is perfect for creating things from scratch, in a relatively basic / easy-to-use environment.
I ended up additionally purchasing VCarve, which makes designing things from scratch in 2.5D very easy (as well as adding 3D elements to custom designs), and also SheetCAM, which is designed for cutting flat materials (anything I do with the drag knives).
Carbide Create and MeshCAM are awesome, but they have limitations that I started running into less than a week after purchasing my Shapeoko 3 (I was doing things they were not designed for).
Having said all of that, if you’re not 100% sure what you’re going to do, @WillAdams list is a perfect starting point.