(Mr MC posting) I build wheels but have in the past bought fully built as its cheaper than buying the bits, but if youve got decent hubs then you can keep the wheels going by replacing rims/spokes as and when needed/wanted. Bought some 717/Hope XCs from CRC a few years ago, then re-built them with 325's when I got into play riding (gaps/drop offs), have just rebuilt them with the 717's for MC's lightweight hardtail.
Also a useful skill if you, say, stack it in the alps and bounce your rear mech into the rear wheel, wrecking a dozen spokes. Ahem.
Congrats, its a great skill to have, I find it very therapeutic and rewarding, and riding on something youve built is a nice feeling (as long as it doesnt collapse…). Just be careful-you might suddenly become very popular with your riding mates 😉