Need Help - First Time Ordering!

I have about 24 items in my warehouse and roughly 20kg total (for some reason the weight when trying to ship comes out to more then what it says under each item why is that?)

Also wondering also if I should or shouldn’t use the shipping expert thing & I did read that the ideal amount to ship is 10 kg so it doesn’t get seized but shipping lowkey is so expensive was curious what are the chances of something bad happening if I ship all in one order.

Then how much do I declare for amount and does it really matter?

Is there anything else I need to know or do?