NGC Slab Size/General Coin Capsule/Slab Questions

Edit:
Why does pressing enter on the main page instantly submit the post?
Well, anyway.
Hello all,

I'd like to know the NGC Slab size in metric, since I am going to buy Leuchtturm EVERSLAB's and wonder if they fit good together on a later stage of my collection.
https://www.ebay.com/itm/QUICKSLAB-Coin-Collection-Capsules-Different-Sizes-Leuchtturm-Coin-Collection-/162984395465

I might want to get into NGC, but I feel that it's too expensive for my taste and I don't know what coins to send to NGC yet. (Current college student, sooo... Spending 50 euro's a coin to get graded is a little much at the moment.)

Else, does anyone know if the slabs from Ebay are any good? The knockoff chinese PCCB slabs? That I 3-d print my own inserts to fit every coin?
https://www.ebay.com/itm/Various-Sizes-PCCB-Protector-Coin-Display-Slab-for-NGC-PCGS-Grade-Collection-Box/172855940557


Thanks in advance,
Dennis