For your first wheels stick to Brass nipples, and spokes no thinner than 14/16g double butted.
While they're just about as strong as brass in use, alloy nipples are more prone to spoke wrench damage and rounding, and as a newbie add another complicarion you can do without.
Same logic regarding thinner spokes, which are more prone to twisting during building, and are enough of a pain that even experienced builders prefer to avoid them.
This is your first pair of wheels, and you'll face enough challenges without going out of your way to make it more difficult. Stick to the basics, and understand that it's easier to walk after you've mastered crawling.
__________________
FB
Chain-L site
An ounce of diagnosis is worth a pound of cure.
Just because I'm tired of arguing, doesn't mean you're right.
“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.