Simple one. If y'all where gonna buy a bunch of inserts and knocks for building arrows, like your just tying to have a lot on hand to use when you wanna try some new shafts or something what size or teo would you pick in general? Like what would be the most common size ?

Thin shafts 3/16 or 1/4 for heavy shafts.

I'd pick a heavier shaft over a lighter one. Speed isn't everything and usually a game animal doesn't care how fast an arrow missed it.

But... to answer your main question, what poundage and draw length are you talking about?

Nothing in particular really gotta
60 lbs diamond compound 26"
Black hunter #50@ 28
Just ordered some 45# limbs for it
A barnet vortex compound shooing like #45
Might be expanding a little more

Got everything from 500 down to 350 spines....trying to get some 200/250's though I shot 350's more then anything

If you're looking for bulk components go with a 5/16" shaft and stick to one brand of arrow The problem with bulk components for arrows is that it lacks consistency. Even among the same brand and model arrow wall thickness will vary according to spine which changes the I.D.. it's not like an AR where you can get components to fit across platforms, it's more like trying to buy a forend that fits a bunch of different shotguns. There's some crossover but not a lot. That's why I suggest sticking with one brand (Easton bow hunters are a good affordable option in every spine from 250 to 500) and then buying bulk components for those specifically.

Also, if 26" is your draw length I wouldn't get in too big of hurry to get anything 250 or stiffer. I have a 29.5" draw and shoot a .250 spine with a 100 grain insert and 200 grain heads and I'm still on the stiff side of things. If you got some 300 spines you could build a very heavy arrow with a ton of f.o.c and still be overspined.

Go with gold tip arrows. You won't need bulk anything. They won't break, bend or shatter. The ID is.246 for regular shafts which is all you need for hunting or tournament shooting. You could go broke buying every new gimmick that comes out. But that's what keeps Archery shops in business I guess. Generally a 400 shaft will work with all the bow weights you listed. A 250 or 200 spine is for heavy poundage bows like 85 pounds with a fairly long draw. Don't waste your money. I sold arrows nationwide for over 20 years.