Question on transplanting starter to pertile and vermiculite mix in net pots

So my plants are just starting to have alot of roots, so I believe it is now time to transplant. I have made a pertile and vermiculite mix. Should i just put the starter plug in the middle of it and poor the rest around it? Or do I need to make the mix a little stronger so it will not fall in through the net pot? Please tell me so I can keep theese plants in a healthy environment. All the best.

Also with an airstone can the roots be in the water? Or do they need to be above the water? The roots have been in the water for about two weeks and they are mostly white. The plant's them selves look great, no yellow spots just perty green.

You can get by with putting the plug right into the net pot media, as long as you are not running recirc or a water pump for top drip. The reality is you should be cleaning the container every couple weeks anyhow. As long as you aren't destroying equipment and plugging filters. Peace & be kind.
Roots in oxygenated water is a good thing

I would use rocks or hydroton if I were you. Dirt and such will just fall through the bottom of the net pot more so than rocks/hydroton.