About to the first oil change since engine rebuild, got a couple questions.

[Lil Ape]

I'm about to do the first oil change since i bought this truck a year ago. Only put maybe 75 miles since it it's engine was rebuilt. I read from many places that you should do your first change before the 100 mile mark. But my first question is how many quarts will I need with a filter change? It's a 350 with stock pan I believe. Isn't it 5 quarts with filter change?

And Next question is the oil itself. Should I use syn since it's a low mile engine, or just stick to cheaper dyno oil? Here in texas, I've always used 10w30 and was recommended to go ahead and use syn since the engine is fresh. But this truck will not be a daily driver by no means. Couple short trips a week at most, And I don't care for the extra miles you'll get out of syn. So I was just going to stick with dyno. But since its a fresh engine, I wanted opinions. It takes me a few months just to put 3k miles on my daily driver.

The engine also has a flat tappet cam, and I know I will need oil with lots of Zinc, The only oil I know of that has a high lvl of zinc is valvoline vr1 I believe. And I prefer to buy oil from the self, not online, so I might me limited. I know amsoil makes awesome stuff, but I cant find it in stores. But If I buy an oil that doesn't have high zinc, would I be okay adding a zinc additive, or is that a bad idea?

I guess my biggest question is, synthetic or conventional lol.